Byzantium in the Crusading movement

The Byzantines were active participants in the crusading movement from its inception in the late 11th century until the Byzantine Empire's collapse in the mid-15th century, acting at times as initiators, allies, or adversaries. As heirs of the Roman Empire, they regarded their state as the centre of the civilised world, ruled by a divinely appointed emperor. During the early Muslim conquests the empire lost extensive territories, though from the 960s some lands, including the city of Antioch, were temporarily recovered. Although relations with Western Christianity were strained after the Schism of 1054, Emperor Alexios I Komnenos appealed to the papacy for aid as Byzantine frontiers faced pressure from Muslim Turkomans. Pope Urban II responded by proclaiming the First Crusade at the Council of Clermont in 1095.

Cooperation between the crusaders and Byzantium proved difficult. Although the crusaders initially helped reconquer territories in Anatolia under agreements with Alexios, he prioritised defending Byzantine lands. Viewing this as a breach, the crusaders established new states in the East—Edessa, Antioch, and Jerusalem—by 1100. Despite defeating Bohemond I of Antioch's anti-Byzantine campaign in 1108, Byzantine attempts to seize Antioch failed. The fourth Crusader state, Tripoli, was established south of Antioch with Byzantine support. Emperors John II Komnenos and Manuel I Komnenos compelled the princes of Antioch to swear fealty and attempted to install an Orthodox patriarch in the city. Byzantine influence in the Crusader states reached its height under Manuel, who also secured an oath of fealty from Amalric of Jerusalem, though joint Byzantine–Jerusalemite attempts to conquer Egypt ultimately failed.

From the outset, crusaders often blamed their failures on the "schismatic" Byzantines' lack of cooperation. In the 1180s treaties between the Byzantines and the Muslim ruler Saladin prompted western accusations that Byzantium supported his attempt to conquer the Crusader states. Preparing a crusade, Henry VI, Holy Roman Emperor, forced Emperor Alexios III Komnenos to levy the extraordinary tax known as the Alamanikon. In 1203 the Fourth Crusade was diverted to Constantinople by the Byzantine pretender Alexios IV Komnenos. His overthrow provoked the Sack of Constantinople and the establishment of the Latin Empire with a Catholic patriarch. Greek resistance was led by Byzantine successor states, first Epirus and from the 1230s Nicaea. Despite papal grants of crusade indulgences to those aiding the Latins, the Nicaeans eventually recovered Constantinople under Michael VIII Palaiologos in 1261. Although the papacy continued to endorse schemes for the Latin reconquest of Constantinople until 1320, all had come to nothing.

The Byzantine Empire was, as the historian Peter Lock notes, "in every sense the heir and embodiment of the Roman Empire", divided into eastern and western halves in 395.^[1] The eastern emperors ruled from Constantinople, refounded in 330 by the first Christian emperor Constantine the Great on the site of ancient Byzantium.^[2] After the fall of the western empire in 476, the Byzantine rulers maintained their claim to universal imperial authority.^[3] This claim was expressed through the concept of translatio imperii and through the imperial title "Emperor and Autocrat of the Romans". The Byzantines called themselves Romaioi ("Romans") and associated their empire with the Oikoumene, or civilised world.^[4]

The emperors were widely regarded as God's representatives on earth. The Christian Church was organised around five major episcopal sees, each headed by a patriarch. Among them, the bishops of Rome, styled popes, enjoyed honorary primacy primarily due to the association of their see with the apostles Peter and Paul, but in imperial thinking were expected to act as loyal officials.^[5] The Byzantine state was administered by an educated bureaucratic elite who recorded their experiences for future generations. Many courtiers were eunuchs, considered especially reliable.^[6] In foreign policy, Byzantium favoured diplomacy over warfare, relying on grants of wealth and titles, along with elaborate ceremonial, to manage rivals and assert imperial authority.^[7]

Byzantine power rapidly waned under pressure from enemies such as the Sasanian Persians, Avars, and Bulgars. From the 630s, the empire was unable to resist the expansion of the emerging Islamic Caliphate and lost the Middle East, Egypt, and North Africa. Islam emerged under Muhammad, whose revelations formed the Quran, regarded by Muslims as God's final and complete message.^[8] Quranic promises of afterlife reward for participation in jihad, or "holy war", helped fuel early Muslim expansion.^[9] As a result of these conquests, the patriarchates of Antioch, Alexandria, and Jerusalem came under Muslim rule, leaving only Rome and Constantinople under Christian control.^[5][10] Christians living under Islam were classified as dhimmis, protected but legally subordinate.^[11]

In western Europe, former Roman territories fragmented into smaller kingdoms ruled largely by Germanic elites. The Franks unified much of Gaul, and under the Carolingians reunited several regions of the former Western Roman Empire.^[12] Byzantine iconoclasm weakened ties with Rome and encouraged cooperation between the papacy and the Carolingians. In 800, the Frankish king Charlemagne was crowned emperor by Pope Leo III. Although iconoclasm was eventually abandoned, the western adoption of the filioque clause about the procession of the Holy Spirit within the Trinity deepened theological divisions with Eastern Christianity.^[13] By the mid-9th century, the Carolingian Empire had fragmented into smaller states, including France and Germany.^[14] A renewed imperial project arose under the German king Otto I, who was crowned emperor by Pope John XII in 962, but the Holy Roman Empire remained politically fragmented.^[15] This diffusion of authority contributed to the rise of a new mounted warrior elite, bound by shared values and later known as knights.^[16][17]

After 963, the Byzantine Empire entered a renewed phase of expansion, as the weakening of the Abbasid Caliphate enabled the recovery of the islands of Crete (961) and Cyprus (965) and the capture of the cities of Antioch (969) and Edessa (1031). Two warrior emperors, Nikephoros II Phokas and John I Tzimiskes, framed their campaigns against Muslim powers as holy wars, a concept that nevertheless remained alien to Byzantine theology.^[18][19] In 975, Tzimiskes declared his intention to liberate the Church of the Holy Sepulchre in Jerusalem but made no attempt on the city. From 1027, treaties with the Fatimid Caliphate—the Abbasids' rivals—recognised the Byzantine emperors as protectors of Christians and confirmed their right to appoint the patriarchs of Jerusalem. These agreements improved security on the route to Jerusalem, encouraging western pilgrimage.^[20]

Military success fostered economic growth, with centres including Corinth, Athens, and Thessalonica. Constantinople, home to more than 350,000 inhabitants, ranked among the world's largest cities and prospered from its position on major trade routes.^[21] At the death of Emperor Basil II in 1025—the period's third great conqueror—Byzantium dominated south-eastern Europe and the Middle East, yet within 50 years faced severe threats on all its frontiers. Scholars disagree over the causes of this decline, pointing to weakened central authority, institutional shortcomings, or intellectual stagnation.^[22] In the late 1020s, cold spells across the Eurasian steppes displaced several Turkic nomadic groups from their homelands: the Pechenegs crossed the Danube in the west, while Turkomans under loose Seljuk leadership took control of the Abbasid Caliphate and raided Anatolia.^[23] The Byzantines lost Antioch in 1078, and Edessa in 1087.^[24]

From the 1040s, Norman warlords attacked Byzantine territory in southern Italy and threatened the Papal States. This prompted Pope Leo IX to seek an alliance with the Byzantines, despite growing tensions between the sees of Rome and Constantinople. By the time papal legates, including Humbert of Silva Candida, reached Constantinople, Leo had died, and negotiations over liturgical differences—especially the western use of unleavened bread in the Eucharist—collapsed into open conflict. On 16 July 1054, the legates excommunicated Patriarch Michael Cerularius, who responded in kind.^[25] Humbert was a leading figure in the Gregorian Reform,^[25] which sought to free the Church from lay control and strengthen papal authority. The movement brought the papacy into conflict with secular rulers during the Investiture Controversy and contributed to Western Christian ideas about just war, including the belief that those who died in a just war were martyrs.^[26][27]

After the Schism of 1054, the newly elected Pope Stephen IX sought to restore relations with Byzantium, but his successor, Nicholas II, instead allied with the Normans.^[28][29] In 1062, Emperor Constantine IX Monomachos exploited the disputed papal succession to send an embassy to Rome proposing an anti-Norman alliance to Antipope Honorius II, who was soon expelled by his pro-Norman rival, Pope Alexander II. According to Bishop Benzo of Alba, Constantine's letter also mentioned an expedition to Jerusalem; if reliable, this represents the earliest recorded reference to a plan about a western military campaign for the city.^[30]

Turkoman pressure intensified along the eastern frontier, culminating in the defeat of Emperor Romanos IV Diogenes by the Seljuk sultan Alp Arslan at the Battle of Manzikert in 1071. This defeat, followed by civil war, enabled large-scale Turkoman settlement in Anatolia.^[31][32] Turkoman advances encouraged renewed rapprochement between Byzantium and western powers, symbolised by the betrothal of Helen, daughter of the Norman ruler Robert Guiscard, to Constantine, heir of Emperor Michael VII Doukas.^[33] In 1074, Pope Gregory VII planned an expedition to support eastern Christians, but it collapsed amid the Investiture Controversy.^[34]

In 1077, the general Nikephoros Botaneiates deposed Michael, prompting Gregory to excommunicate him.^[35] Botaneiates's ally, the Seljuk prince Suleiman ibn Qutulmish, soon occupied much of western Anatolia, including Nicaea. In 1081, Alexios Komnenos, a Byzantine aristocrat, seized the throne, while Guiscard attacked the city of Dyrrachium on the Adriatic coast.^[36] Alexios secured Venetian naval support through commercial privileges and by 1083 forced the Norman withdrawal with Turkoman assistance. By 1094, he crushed the Pechenegs with Cuman support, and also defeated the Cumans, restoring imperial control over the Danube frontier.^[37]

Upon Alexios's accession, Gregory VII excommunicated him, but Gregory's successor Urban II sought to renew relations with the Eastern (or Orthodox) Church. He lifted the excommunication and approached Patriarch Nicholas III of Constantinople, requesting inclusion of his name in the Constantinopolitan diptychs. A synod agreed on condition that Urban formally announce his election and submit a written profession of faith. According to the church historian Aristeides Papadakis, Urban never complied. Nevertheless, Alexios maintained amicable relations with the West for military reasons.^[38] Mercenaries were central to Byzantine armies, and in 1090 Alexios secured a promise from Robert I of Flanders to provide 500 knights.^[39] In 1095, he sent envoys to the Council of Piacenza to seek papal support in mobilising western forces.^[40][41] At this time, as the Byzantininst Ralph-Johannes Lilie notes, the papacy was the only western power "with a vital interest" in aiding Byzantium.^[42]

Shortly after the Council of Piacenza, Pope Urban II travelled to France for a preaching campaign that culminated in the proclamation of the First Crusade at the Council of Clermont on 27 November 1095. He presented the venture as an armed act of penance, promising spiritual rewards that offered relief to knights' troubled consciences, prompting many to "take the cross", sewing cloth crosses on their robes, as a pledge of commitment.^[43][44] Although Urban emphasized the defence of eastern Christians, for most participants the chief aim became the liberation of Jerusalem.^[45]

Emperor Alexios I likely expected limited military assistance under imperial control, but Urban's appeal generated unexpected enthusiasm, leading to the formation of several armies, together exceeding 30,000 armed men and perhaps a further 70,000 non-combatants.^[46][47][48] Urban set 15 August 1096 as the departure date, instructing the crusaders to assemble at Constantinople.^[49] The Byzantine authorities had little time to prepare, and the arrival of large forces beyond imperial control caused alarm. To manage the threat, they adopted what the Byzantinist Jonathan Harris terms a "carrot and stick" strategy, escorting the crusaders with imperial troops to deter attacks while supplying them with provisions.^[50]

Meanwhile, Peter the Hermit, a charismatic preacher, organised a recruitment movement in northern France and eastern Germany. By March 1096 he had gathered over 10,000 followers and departed months before the official crusading forces. From varied social backgrounds, the group included few knights and was largely ill-equipped.^[43][49] Travelling in two contingents, the first, led by the knight Walter Sans Avoir, reached Constantinople without serious incident c. 15 July. The second, led by Peter and knightly captains, clashed with Byzantine forces at Nish over supplies before arriving on 1 August. According to the Gesta Francorum, their plundering of the suburbs led Emperor Alexios to transfer them across the Bosporus into Anatolia. They were almost entirely destroyed by Kilij Arslan I, Sultan of Rum, at the Battle of Civetot on 21 October 1096.^[51][52]

The aristocratically led crusading armies entered Byzantine territory from several directions between October 1096 and April 1097. Hugh of Vermandois, brother of Philip I of France, landed at Dyrrachium; Bohemond of Taranto, son of Robert Guiscard, arrived at Avlona; Godfrey of Bouillon, Duke of Lower Lorraine, travelled overland through Hungary; Raymond of Saint-Gilles, Count of Toulouse, entered via the Dalmatian coast; and a final contingent under Robert of Normandy, Robert II of Flanders, and Stephen II of Blois also disembarked at Dyrrachium. Hugh, whose forces had been scattered by a storm, was escorted to Constantinople under close supervision, while the other armies were guided by Pecheneg mercenaries. Byzantine officials intercepted inter-army communication and required the crusaders to camp outside the city. Emperor Alexios I demanded oaths binding the leaders to restore former Byzantine territories. Although initially resisted—many claiming divine mandate—most eventually complied. Skirmishes with Byzantine troops were frequent, and Bohemond even proposed attacking Constantinople. After the oaths, Alexios rewarded the leaders with gifts.^[53][54]

Between February and April 1097 the armies were transported to Anatolia.^[52] In May they besieged Nicaea with Byzantine support and defeated a relief force under Kilij Arslan. After eight weeks, a Byzantine flotilla severed supply lines across the lake, forcing the defenders to surrender directly to Alexios. The fall of Nicaea opened the route to Antioch. Declining direct command, Alexios appointed his general Tatikios to accompany the army.^[55][56] The campaign weakened Turkomans in western Anatolia and facilitated the Byzantine recovery of Smyrna, Ephesos, and Philadelphia.^[57]

After defeating a major Turkoman force at the Battle of Dorylaeum on 1 July, the crusaders captured several Cappadocian towns, soon transferred to Byzantine control. Lilie argues that these inland territories held little strategic value for them. By contrast, Baldwin of Boulogne, brother of Godfrey of Bouillon, and Tancred, nephew of Bohemond of Taranto, established garrisons in Cilician coastal fortresses seized during an autumn campaign.^[58] The main army began the Siege of Antioch in October. The multi-ethnic city, ruled by the Turkoman emir Yağısıyan under the nominal authority of Ridwan of Aleppo, had formidable defences that prevented a full blockade, while winter shortages strained the besiegers.^[59][60] Tancred rejoined the army, whereas Baldwin advanced eastwards and, with Armenian support, founded the County of Edessa, the first Crusader state, in March 1098.^[61]

In early 1098 Tatikios withdrew to Cyprus for uncertain reasons.^[60] Desertions increased as news spread of a relieving army under Kerbogha, Seljuk governor of Mosul. Among the deserters was Stephen of Blois, whose report to Emperor Alexios at Philomelium portrayed the crusaders' desperate situation and, with rumours of an advancing Seljuk force, contributed to Alexios's decision to abandon his march on Antioch.^[62][63] Despite this, the crusaders captured the city on 3 June with internal assistance and, encouraged by the discovery of the alleged relic of the Holy Lance, defeated Kerbogha on 28 June. Having played a leading role in both victories, Bohemond claimed Antioch, but the leaders sent envoys to Constantinople urging Alexios to assume control, warning that failure to do so would void their earlier oaths.^[64][65]

The advance towards Jerusalem was delayed by the summer heat. Bohemond began ruling Antioch, granting property and commercial privileges to the Genoese. By early November 1098 he had convinced most crusader leaders, except Raymond, that Byzantine support would not arrive. They therefore recognised his claim to the city, while requiring him to withdraw from the nearby port of Laodicea, regarded as Byzantine territory. When the crusade resumed in November, Bohemond exploited the army's departure to consolidate the Principality of Antioch.^[66][67] In March 1099 Byzantine envoys demanded Antioch's surrender but were rebuffed. Their complaints at the crusader camp at the fortress of Arqa were dismissed on the grounds that Alexios had failed to honour his commitments. Although they promised the Emperor's arrival by late June and offered substantial gifts, only Raymond supported them. The crusaders continued their advance and captured Jerusalem on 15 July.^[68][69] Godfrey of Bouillon became the city's first crusader ruler, while his brother Baldwin was crowned the first King of Jerusalem on Christmas Day 1100.^[70]

The establishment of the Crusader states transformed the political landscape of the Middle East. Antioch was especially significant as a major commercial centre and leading ecclesiastical see.^[71] Its strategic position made any Byzantine campaign against Jerusalem or Edessa impracticable.^[72] Although Jerusalem had been lost centuries earlier, successive emperors continued to claim responsibility for protecting its holy sites. By contrast, the Byzantines did not challenge the Frankish occupation of Edessa.^[73] In 1099–1100 Catholic clerics were appointed to the sees of Jerusalem and Antioch in disregard of imperial prerogatives. In Jerusalem the death of the Orthodox patriarch Symeon II eased the appointment; in Antioch Bohemond exiled the patriarch John the Oxite to install a Latin incumbent. The Byzantines rejected these appointments and instead named Orthodox patriarchs resident in Constantinople, creating parallel Catholic and Orthodox successions in both sees.^[74]

During the First Crusade a Byzantine force seized Laodicea, threatening Antioch. Bohemond allied with Archbishop Daimbert of Pisa, who arrived in August 1099 with a fleet that had plundered Byzantine islands. Laodicea was eventually taken, with Byzantine approval, by Raymond of Saint-Gilles after his return from the Jerusalem campaign. Imperial forces subsequently secured Cilicia, and their position was strengthened when Bohemond was captured by Turkomans in August 1100.^[75] Early the following year Tancred became regent of Antioch and seized Cilician towns and Marash from the Byzantines.^[76][77]

Another wave of crusading armies reached Constantinople in spring 1101, led by nobles and prelates including Anselm of Milan, William IX of Aquitaine, and Welf of Bavaria. Alexios required their leaders to swear an oath to restore reconquered imperial territories before transporting them into Anatolia, appointing the general Tzitas to escort them. Although the armies were eventually destroyed by Turkoman coalitions, they recovered Ankyra for the Byzantines.^[78][79] Raymond, who had joined the expedition at Constantinople, was among the few leaders to survive. He withdrew from Laodicea and, with Byzantine support, prepared campaigns against Tortosa and Tripoli south of Antioch. Laodicea was soon seized from the Byzantines by Tancred (likely in early 1103, according to Lilie).^[80]

Bohemond was held captive by the Danishmend emir Gazi Gümüshtigin, who released him for 100,000 nomismata. Alexios again demanded the cession of Antioch, but Bohemond refused.^[81][82] On 7 May 1104 forces from Antioch and Edessa were defeated by a Turkoman coalition at the Battle of Harran. Baldwin of Bourcq, successor to Baldwin of Boulogne in Edessa, was captured, and Bohemond appointed Tancred to rule the county.^[83] Meanwhile Byzantine forces regained Laodicea and several Cilician towns, prompting Bohemond to seek Western support and return to Europe by the end of the year.^[84]

Bohemond secured the support of Pope Paschal II for a new crusade and raised a force of French and Italian knights. In autumn 1107 he crossed the Adriatic to attack Dyrrhachium. Anticipating the campaign, Alexios I recruited Turkoman mercenaries, mobilised imperial troops, and obtained Venetian naval assistance. Avoiding battle, the Byzantines blockaded Bohemond's army, cut its supply lines, and forced his surrender in September 1108.^[85][86] Under the Treaty of Devol, Bohemond declared himself "the loyal man" of Alexios. In return for recognition of his lifetime rule over Antioch and nearby territories, he undertook to arrange Tancred's withdrawal from other conquered lands and accept an Orthodox patriarch for Antioch.^[87] Historians differ in their assessments, but the treaty suggests Alexios sought recognition of his suzerainty over Antioch but accepted the Normans' rule.^[88]

The treaty was never implemented: Bohemond did not return to Antioch and Tancred ignored its provisions, expanding into Cilicia and capturing Laodicea.^[89] Alexios responded by encouraging Seljuk attacks, placing the northern Crusader states under pressure.^[90] In July 1109 a coalition of Frankish rulers captured Tripoli and granted it to Bertrand, son and successor of Raymond of Saint Gilles, who had sworn fealty to Alexios.^[91][92] Alexios later sought support from Bertrand and Baldwin I of Jerusalem against Tancred, offering financial inducements, but both refused. After Bertrand's death in 1112, his son Pons renewed his oath of fealty to Alexios.^[93] Tancred died in the same year and was succeeded by his nephew Roger of Salerno.^[94]

Emperor Alexios I died of illness on 15 August 1118. His son and successor, John II, initially faced a conspiracy led by his sister Anna Komnene and invasions on several fronts, limiting Byzantine involvement in the affairs of the Crusader states.^[95] By the time of his accession a Byzantine envoy, Ravendinus, had arrived in Antioch to negotiate a marriage alliance, according to the chronicler Orderic Vitalis. The following year Ravendinus was present at the Battle of the Field of Blood, where the Turkoman ruler Ilghazi inflicted a crushing defeat on Roger of Salerno, who was killed.^[96][97] Antioch survived largely through the intervention of Baldwin II, the new king of Jerusalem, who assumed the regency for Bohemond's absent son, Bohemond II.^[88]

John refused to confirm Venetian commercial privileges, provoking a Venetian naval attack on the island of Corfu during the Venetian Crusade to the Holy Land in 1123, followed by raids on Aegean islands the next year as their fleet returned. Peace was restored in 1126 when John confirmed these privileges.^[98][99] In the same year Bohemond II arrived in Antioch and married Alice, Baldwin II's daughter, but was killed by Danishmendid forces in 1130. Baldwin II again assumed the regency, this time for Bohemond and Alice's six-year-old daughter Constance. His death the following year triggered conflict between his successor and son-in-law, Fulk of Anjou, and Alice.^[100] Meanwhile, the Turkoman general Zengi united Mosul and Aleppo and pursued expansion in Syria.^[101] Taking advantage of the instability, an Armenian ruler in Cilicia, Leo, seized coastal towns from Antioch.^[102] In 1136 Antiochene envoys proposed Constance's marriage to John's youngest son Manuel, but Fulk instead arranged her marriage to the French noble Raymond of Poitiers.^{[103][104][105]}

In the early 1130s John's younger brother, the sebastokrator Isaac Komnenos, defected from the Byzantine Empire and sought support among its eastern Muslim and Christian neighbours. Lilie argues that Isaac's ultimately unsuccessful search for allies heightened John's concerns about the Middle East.^[106] Three 12th-century historians offer differing explanations for John's decision to launch a campaign there: John Kinnamos and William of Tyre emphasise the issue of Constance's marriage, while Michael Choniates highlights Armenian expansion.^[104][107]

In summer 1137 John invaded Cilicia, capturing coastal towns and forcing Leo to take refuge in the Taurus Mountains. He then advanced on Antioch, compelling Raymond to submit in September.^[108][109] The terms of their agreement remain unclear: Kinnamos and Choniates describe Raymond's acceptance of Byzantine suzerainty, while William of Tyre records a promise to cede Antioch in exchange for Aleppo, Shaizar, Hama, and Homs, to be conquered with Byzantine support. In May 1138 Raymond and Joscelin II of Edessa joined John's campaign against Aleppo, which failed, leading the army to attack Shaizar. Its ruler secured peace by paying an indemnity. After the expedition John made a triumphal entry into Antioch, where Raymond again acknowledged him as overlord.^[110]

In autumn 1142 John returned to northern Syria aiming at conquest. He first attacked Turbessel, seat of Joscelin, forcing him to surrender a daughter as hostage. John then advanced on Antioch and, according to Kinnamos, demanded the city, intending to grant it as an appanage to Manuel. Raymond refused, arguing—according to William of Tyre—that he ruled in his wife's right and could not dispose of the principality. John withdrew to winter in Cilicia, sending envoys to Fulk to announce a planned pilgrimage to Jerusalem, from which Fulk dissuaded him.^[111][112] John died in a hunting accident on  April 1143.^[113] The Byzantinist Paul Magdalino observes that his death prevented "the most ambitious" Byzantine attempt to restore the pre-Islamic empire since the 10th century.^[114]

John was succeeded by Manuel, the younger of his surviving sons. Exploiting the uncertain succession and a Seljuk invasion, Raymond demanded several Cilician towns. His incursion was repelled by a Byzantine army, while a fleet raided the Antiochene coast.^{[115][116][117]} On 24 November 1144 Zengi besieged Edessa. Raymond was unable to send relief and the city fell in late December.^[118] The loss of Edessa forced Raymond to seek reconciliation with Byzantium, leading to a visit to Constantinople where he swore fealty to Manuel.^[115][116] Meanwhile the Cilician Armenians benefited from the changing situation, as Leo's son Thoros II united much of Cilicia under his rule by the end of the decade.^[119]

The fall of Edessa led Pope Eugenius III to proclaim the Second Crusade in December 1145. The campaign was led by Conrad III of Germany and Louis VII of France, both of whom marched through Byzantine territory. As during the First Crusade, news of the expedition caused concern in Constantinople.^[120] To secure an anti-Norman alliance, Manuel married Conrad's sister-in-law, Bertha of Sulzbach, in early 1146.^[121] Byzantine envoys were sent to both rulers to negotiate provisions for their armies, although clashes with local populations during the march across the Balkans proved unavoidable.^[122] In summer 1147, a naval raid by Roger II of Sicily against the Ionian Islands and Greece heightened Byzantine fears of a coordinated western attack on the empire.^[123][124]

The Germans reached Constantinople in September and crossed the Bosporus into Anatolia without waiting for the French. Ignoring Manuel's advice to advance through western Anatolia, they engaged the Sultanate of Rum and suffered a decisive defeat at the Battle of Dorylaeum. Conrad narrowly escaped into Byzantine territory and, owing to illness, resumed the crusade only the following spring, sailing to Acre.^[125][126]

The French arrived in October 1147.^[123] A faction influenced by Bishop Godefroy of Langres urged Louis VII to attack Constantinople in retaliation for the expulsion of Catholic clergy from Byzantine Cilicia. According to the chronicler Odo of Deuil, Manuel persuaded the French to continue by circulating false reports of a German victory over the Seljuks. Although Manuel secured oaths from French leaders to surrender reconquered imperial territories in exchange for supplies, the crusaders relied heavily on plundering the local population. Consequently local Greeks supported the Turkomans, who repeatedly harassed the French during their march across western Anatolia. Weakened by these attacks, Louis and several leaders sailed from Attalia to Antioch aboard Byzantine ships, leaving the main army behind; during its march towards Syria it was almost entirely destroyed by Turkoman forces.^[127]

After reaching the Kingdom of Jerusalem, the remaining crusaders besieged Damascus, but the operation failed in July 1148.^[128] On his return to Germany Conrad III renewed the anti-Norman alliance with Manuel during a meeting in Thessalonica in 1148–49. By contrast, the French adopted a hostile stance towards Byzantium, accusing it of duplicity, inadequate provisioning, and tacit collaboration with the Seljuks, which they blamed for the crusade's failure.^[129]

In the aftermath of the Second Crusade, Emperor Manuel faced invasions, as well as internal rebellions.^[130] In the east, Nur al-Din, Zengi's successor in Aleppo, launched raids against the Crusader states. Raymond of Antioch was killed at the Battle of Inab in 1149, and in 1150 Joscelin II of Edessa was captured. His wife, Beatrice of Saone, sold the county's remaining lands to Manuel for an annuity, but within a year Nur al-Din had conquered them.^[131][132] To strengthen Byzantine influence in Antioch, Manuel proposed that Princess Constance marry the Kaisar John Roger, yet, backed by Antioch's citizens, she instead wed the French knight Raynald of Châtillon in 1153. Meanwhile, an imperial army was defeated by Thoros II of Cilicia. Raynald launched a campaign in Byzantine service in Cilicia but, deeming his reward unduly delayed, allied with Thoros and raided Cyprus.^[133][134]

In 1158 Manuel made peace with William II of Sicily,^[135] enabling a firmer policy towards the Crusader states, increasingly threatened by Nur al-Din's union of Damascus and Aleppo. Western crusading zeal had waned, and reinforcements to Syria were inadequate.^[136][137] In 1157 Baldwin III of Jerusalem sent envoys to Constantinople proposing a marriage alliance; Manuel chose his niece Theodora as Baldwin's bride and granted a generous dowry of 100,000 nomismata.^[136][138] The alliance proved advantageous to Manuel. When he launched a punitive campaign against Cilicia and Antioch, Baldwin consistently supported him. In early 1159 Raynald was compelled to swear fealty to the Emperor and accept the replacement of Antioch's Latin patriarch with an Orthodox prelate. Present at the negotiations, Baldwin helped reconcile Manuel and Thoros, who surrendered the Cilician coastal towns and acknowledged Byzantine suzerainty. Manuel's ceremonial entry into Antioch symbolised imperial supremacy: Baldwin rode behind him without royal insignia, and Raynald acted as marshal.^[139] Manuel also pledged support against Aleppo, yet the projected joint campaign was abandoned after he concluded peace with Nur al-Din in return for Christian captives and an alliance against the Seljuks of Rum. In the end, Raynald failed to install an Orthodox patriarch.^[140]

In 1160–61 Raynald was captured by Turkomans, and Baldwin III appointed Aimery, the Latin Patriarch of Antioch, as regent for the young Bohemond III, Constance's son. Widowed in 1159, Manuel sought a Frankish bride; though Baldwin proposed Melisende of Tripoli, he chose Maria, Bohemond's sister. Offended, Raymond III of Tripoli raided Byzantine territory with his fleet.^[141] After Baldwin III's death in 1163, his brother Amalric succeeded him. He warned Louis VII of France that without western aid the Crusader states would fall to Nur al-Din or Byzantium, though such assistance never arrived.^[142][143]

In Lilie's view, Emperor Manuel's intervention in 1159 reassured the Franks that he would not undermine Nur ad-Din, while signalling to Nur ad-Din that Byzantium would block any attempt to seize Antioch; consequently, both sides turned their attention to the weakening Fatimid Caliphate.^[144] Amalric of Jerusalem invaded Egypt in September 1163, and in response Nur ad-Din dispatched his Kurdish general Shirkuh the following year.^[145] He also invaded Antiochene territory, defeating a Byzantine–Antiochene–Cilician Armenian coalition at the Battle of Harim. According to William of Tyre, fear of Byzantine intervention deterred an assault on Antioch and led instead to Bohemond III's ransom, which Manuel financed in return for his agreement to install the Orthodox patriarch Athanasius I Manasses in Antioch.^[146][147]

Concluding that the Crusader states depended upon Byzantine protection, Amalric sent an embassy to Constantinople in 1165 seeking an imperial bride. Around the same time, Manuel's cousin Andronikos Komnenos seduced Manuel's sister-in-law Philippa in Antioch and embezzled imperial funds before fleeing to Jerusalem. Unaware of his actions, Amalric granted him Beirut as a fief; Andronikos then began an affair with his niece Theodora, Baldwin III's widow.^[148] In 1167 Amalric married Manuel's great-niece Maria Komnena, swore fealty to the Emperor, and acknowledged him as protector of the holy places. With Byzantine support, churches and monasteries were restored throughout the kingdom.^[149][150] When Manuel demanded Andronikos's extradition, he and Theodora fled to Nur ad-Din.^[151]

Fearing Amalric's invasion, the Fatimid caliph al-Adid appointed Shirkuh vizier in early 1169, and after his death his nephew Saladin.^[150] In late summer a Byzantine fleet of more than 150 galleys reached Cyprus, yet delays by the Jerusalemite army left it undersupplied, and a joint assault on the Egyptian port of Damietta failed in January 1170. Lilie suggests that Amalric participated half-heartedly, opposing Byzantine expansion.^[152] That year an earthquake destroyed the sanctuary of Antioch Cathedral and killed the Orthodox patriarch, prompting Bohemond to restore the Latin patriarch.^[147] A Jerusalemite embassy sought western aid but achieved nothing amid conflicts between France and England and between Emperor Frederick I and the papacy. In March 1171 Amalric travelled to Constantinople and, according to Kinnamos, swore fealty to Manuel.^[153][154] Soon afterwards, following a Venetian attack on the Genoese quarter in Constantinople, Manuel ordered the arrest of Venetians across the empire, provoking prolonged conflict.^[155]

After al-Adid's death in September 1171, Saladin abolished the Fatimid Caliphate, though his relations with Nur ad-Din deteriorated. Nur ad-Din died in May 1174, leaving an underage son al-Salih. Amalric died two months later, and Jerusalem passed to his leprous son Baldwin IV. By year's end Saladin had secured Damascus, Homs and Hama but failed to take Aleppo.^[156] Renewed war with the Seljuks of Rum culminated in Manuel's defeat at Myriocephalum, though Byzantine forces routed Turkoman raiders the following year.^[157] In August 1177, despite preparations for a joint Egyptian campaign, the Jerusalemite council rejected the plan after a Byzantine fleet reached Acre, and no further action followed, though negotiations continued until Manuel's death on 24 September 1180.^[158]

Emperor Manuel was succeeded by his eleven-year-old son, Alexios II Komnenos, who ruled under the regency of his mother, Maria of Antioch. Her authority was soon challenged by rivals, notably Alexios's stepsister Maria. The empire's enemies exploited the unrest: the Seljuks of Rum and Ruben III of Cilicia advanced in southern Anatolia, while Bohemond III of Antioch repudiated his Byzantine wife.^[161][162] In April 1182 Andronikos Komnenos seized power in a coup amid popular unrest, during which a mob sacked Constantinople's Italian quarter and massacred most of its inhabitants. The atrocity provoked strong anti-Byzantine feeling in the Crusader states and western Europe.^[163][164] Andronikos purged his opponents, executed Alexios, restored the Venetians and offered compensation for confiscated property. Early in 1185 Manuel's grandnephew Isaac Komnenos seized Cyprus and assumed the imperial title, and in June William II of Sicily invaded from the west.^[165]

A letter by an anonymous Western writer, preserved in Magnus of Reichersberg's chronicle, claims that William's invasion led Andronikos to ally with Saladin against the Seljuks of Rum and the Crusader states. As no other source confirms this, its reliability is doubtful. Harris suggests it may instead reflect Saladin's promise, if he captured Jerusalem, to recognise Andronikos as protector of the holy places and local Christians.^[166] Nevertheless, as Magdalino notes, under Andronikos and his successors Byzantium "opted out of the crusading movement".^[167] William's capture of Thessalonica in August 1185 prompted another purge in Constantinople. Isaac Angelos, one intended victim, rebelled with popular support; Andronikos was lynched and Isaac proclaimed emperor. The army soon recovered Thessalonica, massacred thousands of Normans and retook Dyrrachium. Isaac made peace with the Seljuks and Hungary, but an extraordinary levy sparked a revolt amongg Bulgarians and Vlachs in the Balkans.^[168]

On 4 July 1187 Saladin destroyed the army of the Kingdom of Jerusalem the Battle of Hattin.^[169] Magnus of Reichersberg's correspondent blamed Emperor Isaac II Angelos, alleging he had urged Saladin to take Jerusalem, but Harris dismisses this as "demonstrably false", though rising anti-Byzantine feeling made it plausible in the West. By year's end Saladin held Jerusalem and most of the kingdom. Rumours spread across Catholic Europe of an alliance with Isaac, while Muslim and eastern Christian sources mention only talks about a mosque in Constantinople and transferring the Church of the Holy Sepulchre to the Orthodox Patriarch of Jerusalem.^[170]

After news of Hattin reached Rome in October 1187, Pope Gregory VIII proclaimed the Third Crusade. Emperor Frederick I, Richard I of England and Philip II of France took the cross, though only Frederick went overland, negotiating with anti-Byzantine leaders such as the Serbian Stefan Nemanja. His past conflicts with Byzantium caused alarm in Constantinople, prompting Isaac to send an embassy. An agreement at Nuremberg in 1188 granted the Germans free passage and access to markets, while Frederick promised peaceful transit.^[171][172]

Despite the agreement, when the German crusaders entered Byzantine territory in July 1189, supplies were inadequate. Frederick's envoys were arrested in Constantinople, and a Byzantine embassy demanded hostages, accusing him of seeking to place his son, Frederick of Swabia, on the imperial throne. Frederick seized Philippopolis, and his son defeated a nearby Byzantine force. The crisis deepened western suspicions of Isaac's alliance with Saladin, and rumours spread that the Byzantines were poisoning the crusaders. Frederick even considered attacking Constantinople. Although Isaac informed Saladin of the crusaders' arrival, Harris argues this reflected traditional Byzantine diplomacy rather than obstruction. A settlement was eventually reached, and in March 1190 the Germans crossed into Anatolia via the Dardanelles, avoiding Constantinople.^[173][174] They captured Konya, capital of Rum, but Frederick's drowning in the River Saleph on 10 June ended the expedition, and only a few of his forces reached Syria.^[175]

Departing on crusade in July 1190, Richard and Philip wintered in Sicily before sailing on in spring 1191.^[176] The French fleet reached Syria safely, but the English was scattered by a storm and regrouped at Cyprus. Richard seized the island within three weeks, imprisoned the self-proclaimed emperor Isaac Comnenus, and sold Cyprus to the Knights Templar for 100,000 bezants. When they failed to quell a local revolt, they returned it; Richard then sold it to Guy of Lusignan, former King of Jerusalem, for 60,000 bezants. The first Byzantine territory permanently taken by crusaders, Cyprus remained under Lusignan rule for over three centuries.^[177][178] Despite tensions between Richard and Philip, the Third Crusade restored parts of the Kingdom of Jerusalem, notably through the recapture of Acre and Richard's victory at Arsuf.^[179]

Emperor Henry VI, son and successor of Frederick I, revived his father's crusading plans. In 1194 he pressed his wife Constance's claim to Sicily, despite Isaac II's efforts to counter him by renewing Genoese and Pisan privileges and marrying his daughter Irene to Roger, heir to Constance's rival, Tancred. After the German conquest of Sicily, Henry married Irene to his brother, Philip of Swabia.^[180] Meanwhile, Bulgarian and Vlach rebels, led by the brothers Peter and Asen and aided by Cumans, secured the Balkan Mountains; the brothers assumed the title of tsar (emperor). Isaac was deposed and blinded in April 1195 by his brother, Alexios III Angelos, who soon faced a pretender, continued raids and army mutinies.^{[181][182][183]}

Henry took the cross at Bari in 1195 and demanded access to Byzantine ports, ships and 5,000 pounds of gold, threatening invasion. Unable to resist, Alexios agreed to pay 1,000 pounds and imposed the Alamanikon ("German tax"), even stripping imperial tombs.^[184][182] Leo of Cilician Armenia and Aimery of Cyprus also accepted Henry's suzerainty for royal titles.^[185] Byzantium was spared by Henry's sudden death and the ensuing German civil war.^[186][187] Alexios also maintained what Lilie calls "empty claims", as shown by a 1198 chrysobull granting Venetians privileges in Antioch and Laodicea.^[188][189]

In the year of his accession (1198), Pope Innocent III proclaimed the Fourth Crusade. His appeal was warmly received among French nobles, including Theobald III of Champagne and Baldwin IX of Flanders.^[190][191] Amid growing anti-Byzantine feeling in western Europe, Emperor Alexios III wrote to the Pope in February 1199, voicing hope for Jerusalem's recovery without pledging participation, and requesting an ecumenical council to heal the schism.^[192] Innocent urged reunion under papal supremacy and called upon the Emperor to aid the expedition.^[193]

In April 1201 the crusade leaders concluded a treaty with Venice, agreeing to pay 85,000 marks by April 1202 for ships to carry over 33,000 crusaders and their provisions. That summer they chose Boniface I of Montferrat as the expedition's paramount leader. Boniface's brother, Renier, Emperor Manuel's son-in-law, had fallen victim to the purge under Andronikos I.^[194][195] When the crusaders could not pay in full, Venice deferred 35,000 marks in return for help capturing Zara, a Dalmatian town under Hungarian rule. Meanwhile Alexios Angelos, son of the deposed Emperor Isaac II, fled Constantinople to seek western aid against Alexios III. In January 1203 he offered to submit the Byzantine Church to Rome, pay 200,000 marks, and join the crusade with 10,000 troops if his father were restored.^[196][197]

Despite opposition from the rank and file, the principal leaders—Boniface, Baldwin, and the Venetian doge Enrico Dandolo—accepted Alexios's offer for strategic reasons, and the fleet reached Constantinople on 24 June 1203. Although Pope Innocent had warned Alexios III in November 1202 that "the fire in distant regions" might spread to Byzantine territory if he withheld support, he expressly forbade an attack on the city in June 1203; his envoys, however, did not reach the crusaders.^[198][199] The imperial army, numbering nearly 20,000, matched the crusaders in strength, Alexios III fled on 17 July after the Venetians seized towers along the Golden Horn. Isaac II was restored the next day, and on 1 August his son was crowned co-emperor as Alexios IV. He paid 100,000 marks andin a letter issued jointly with Patriarch John X of Constantinople, acknowledged papal primacy.^[200][201]

Alexios IV did not pay the remaining 100,000 marks, likely because fires during the siege devastated Constantinople's commercial quarters, reducing customs revenues, while territories beyond the capital remained under Alexios III. Though the crusaders expelled his uncle from Thrace, his heavy taxation and tensions with them made him unpopular. On 29 January 1204 Alexios Doukas Mourtzouphlos seized power as Alexios V. The crusaders denounced him as a usurper who had slain his lawful sovereign and, during a skirmish, captured a richly adorned icon of the Mother of God, which they took as a sign that divine favour had passed to them.^[202]

In March 1204, as they prepared to renew the siege of Constantinople, the crusader leaders and the Venetians agreed to elect a Latin emperor, who would receive a quarter of the city and empire. Venice was to take another quarter of the city and three-eighths of the empire, the rest to be divided as fiefs. If a crusader became emperor, a Venetian would be patriarch, and conversely.^[203][204] After a failed assault and the expulsion of prostitutes from their camp, a second attack on 12 April succeeded, and Alexios V fled. A three-day sack followed: thousands were killed, women raped, and churches desecrated. The plunder, worth 800,000 marks^[205]—equivalent to the ten-year income of what Tyerman describes as "a substantial western state".^[206] To the crusaders, victory signified divine favour against a schismatic foe unwilling to defend the holy places. Strategically, control of the wealthy Byzantine Empire promised to strengthen the Crusader states. Pope Innocent echoed this confidence, declaring that through their conquest "the Holy Land might be more easily liberated from pagan hands", when he authorised them to abandon the crusade.^[207]

Boniface of Montferrat married Margaret of Hungary, widow of Emperor Isaac II, to bolster his claim to the imperial throne. Venetian opposition to the pro-Genoese Boniface, however, secured the election of Baldwin of Flanders as first Latin Emperor of Constantinople, crowned on 16 May 1204.^[208][209] The Venetians then installed Thomas Morosini as Latin Patriarch. The victors formalised the partition of the Byzantine Empire, though much territory remained unconquered.^[210] Thereafter, the Latins seized extensive Byzantine lands, founding states such as the Kingdom of Thessalonica, the Principality of Achaea and the Duchy of Athens. The Latin Empire became, in the historian David Jacoby's phrase, "a mosaic of political entities", linked by shifting and intricate networks of vassalage.^[211] Meanwhile, the Venetians took Crete, several Ionian islands and Dalmatian ports, excluding their Genoese and Pisan rivals from trade within the Empire.^[212]

Initially, the Latins encountered little resistance, and many locals welcomed them as protectors against enemies such as the Bulgarians. By contrast, the traditional Byzantine elite, associated with onerous taxation, were widely blamed for the empire's collapse. Although Catholic bishops replaced Orthodox prelates in Latin-held dioceses, parish life remained largely unchanged.^[213] In 1205, the Bulgarians' victory at the Battle of Adrianople and the capture of Emperor Baldwin I exposed the fragility of Latin rule, allowing the consolidation of three Byzantine successor states. The first, the Empire of Trebizond, was founded in early 1204 by Alexios I and David Komnenos, grandsons of Emperor Andronikos I, and expanded westwards along the Black Sea coast of Anatolia. They soon clashed with the Empire of Nicaea, established in western Anatolia by Theodore I Laskaris, son-in-law of Emperor Alexios III. The third, the Despotate of Epirus, was founded by Michael I Komnenos Doukas, a relative of the Angelos emperors.^[214] The Latin Empire was preserved by Baldwin's brother and successor, Emperor Henry, who secured and extended its frontiers in Thrace and Anatolia through campaigns against the Bulgarians and the Nicaeans.^[215]

After the Orthodox patriarch John X died in exile in 1206, Constantinople's Orthodox clergy sought Pope Innocent III's approval to elect a successor, but Latin opposition prevented this. Eventually, Theodore I secured the election of Michael IV at Nicaea in 1208, and the new patriarch soon crowned him emperor.^[216] The Nicaean rulers claimed to be the lawful successors of the Roman emperors, yet a new identity emerged at their court emphasising Greek ancestry. This found expression in a rhetorical style that replaced "Romans" with "Hellenes", asserting cultural superiority over the Latins.^[217] In 1209, Patriarch Michael urged Nicaean soldiers to fight their "unjust and arrogant enemies", promising absolution to those who fell, thereby in practice adopting the Catholic concept of crusading in clear contradiction with traditional Byzantine theology.^[218]

The survival of the Latin Empire depended largely on western assistance, secured chiefly through active papal support. A letter of 7 November 1204 from Pope Innocent III already refers to "lay crusaders" serving in the Latin army "in hope of ... the indulgence granted by the Apostolic See".^[219][220] Crusading zeal could readily be directed against the Empire's enemies, as the Crusader states' position consolidated due to rivalries among the Ayyubid rulers (kinsmen and successors of Saladin).^[221] Innocent proclaimed the first crusade in support of the Latin Empire following their defeat at the Battle of Adrianople. He warned that a Byzantine restoration would threaten western access to the Holy Land, recalling earlier hostilities, and released participants from prior pilgrimage vows except those undertaken to the Holy Land, thereby establishing a precedent for the commutation of vows. The expedition was defeated near Dyrrhachium by Theodore Komnenos Doukas, brother and successor of Michael of Epirus.^[222]

Epirus assumed leadership of anti-Latin resistance when Theodore defeated a crusading force led by Peter of Courtenay, Emperor Henry's successor, in 1217. After capturing Thessalonica in 1224 and ending the Latin kingdom, Theodore was crowned emperor c. 1225 by Archbishop Demetrios of Ochrid to press his claim to Constantinople. His expansion ended in 1230 when Ivan Asen II of Bulgaria defeated him at the Battle of Klokotnitsa.^[223][224] Meanwhile, the Nicaean emperor John III Vatatzes regained much of north-western Anatolia from the Latins and, allied with the Bulgarians, reduced the Latin Empire by 1235 to little beyond Constantinople in Thrace.^[225][226] Elected in 1227, Pope Gregory IX tried to redirect crusading zeal to defend the Latin Empire, urging English, French, and Hungarian crusaders bound for the Holy Land to fight Greeks and Bulgarians in the Aegean, and backing John of Brienne, co-ruler for the underage emperor Baldwin II, in raising troops for Constantinople's defence.^[227] However, his efforts to rally forces against anti-papal Christians by granting indulgences grew unpopular, as shown by Richard of Cornwall's oath to fulfil his vow only in the Holy Land despite papal pressure.^[228] From 1239 onwards, the papacy concentrated on urging the vassals of the Latin Empire, including Geoffrey II of Achaea, to assume responsibility for the defence of Constantinople, while underwriting these efforts by imposing a tax on the revenues of the western clergy.^[229]

The diminished Latin Empire, lacking substantial tax revenues, verged on bankruptcy from the 1230s. Baldwin melt down first the city's gold and silver treasures, then the ancient bronze statues, and finally the lead roofs of the palaces. The sale or pawning of relics also became an important source of income: the relic of the Crown of Thorns was first pledged to the Venetians and later sold to Louis IX of France, who built the Sainte-Chapelle in Paris to house it.^[230]

Ivan Asen died in 1241, and during the reign of his underage son, Kaliman I, Bulgaria lost territories along its frontiers. In 1242, the Mongols invaded Bulgaria and the Sultanate of Rum, swiftly reducing them to tributary states.^[231][232] Exploiting the resulting weakening of Nicaea's rivals, John III Vatatzes pursued an expansionist policy, capturing several Macedonian towns and Thessalonica in 1246. As a result, Nicaea controlled as much territory in Europe as in Anatolia, effectively surrounding Constantinople.^[233] Hoping to recover Constantinople peacefully from the Latins, Vatatzes—following earlier precedents—entered into negotiations with Pope Innocent IV concerning a union of the churches. Although compromises were reached on several issues, the talks ended with the deaths of both Vatatzes and Innocent in 1254.^[234][235]

Vatatzes was followed on the throne by his epileptic son, Theodore II Lascaris, whose death in 1258 left the empire to his seven-year-old son, John IV Lascaris. The regency was seized by the aristocrat Michael Palaiologus, who proclaimed himself co-emperor as Michael VIII in early 1259. Nicaea's enemies attempted to exploit the succession crisis, but the Nicaean army defeated a coalition of Epirote, Achaean and Sicilian forces at the Battle of Pelagonia. After a failed assault on Constantinople in spring 1260, Michael concluded a treaty with Genoa, granting commercial privileges in return for assistance. The city was eventually taken by surprise when the general Alexios Strategopoulos entered the city on 25 July 1261 during the absence of much of the Latin garrison and the Venetian fleet. Emperor Baldwin II fled aboard a Venetian vessel.^[236][237]

Michael VIII Palaiologos was crowned emperor in Hagia Sophia on 15 August 1261. He reached an agreement with William II of Achaea, captured at Pelagonia, who secured his release by ceding the fortresses of Grand Magne, Mistra and Monemvasia to the Byzantines.^[238][239] The child emperor John IV was deposed and blinded on Michael's orders, prompting Patriarch Arsenius of Constantinople to excommunicate him.^[240]

After the Greek recovery of Constantinople, Pope Urban IV proclaimed a crusade against the restored Byzantine Empire, but it gained little support, and French and Spanish clergy refused to fund it.^[241] The Pope released William from his oath to Michael to encourage an alliance with Venice and the exiled emperor Baldwin II, but the Byzantines, aided by Genoa, seized Aegean islands and captured Achaean fortresses. The long conflict drained the treasury, leading Michael to seek reconciliation with Venice in 1265.^[242]

Meanwhile, the Mamluks replaced the Ayyubids as the dominant Muslim power in the Middle East. The Mamluk sultan Baybars captured castles from the Crusader states and took Antioch in 1268. Michael pursued what Harris describes as "versatile diplomacy" making treaties with rival powers. His agreement with Baybars strengthened commercial contacts, confirmed his right to appoint the Orthodox patriarch of Jerusalem, and ensured the supply of Cuman troops to the Mamluks. He also allied with Mongol rulers, marrying his daughters to Abaqa of the Ilkhanate and Nogai from the Golden Horde.^[243][244]

Michael VIII soon faced a new adversary when Charles I of Anjou, brother of Louis IX of France, conquered Sicily with papal support in 1266. Two years later Charles concluded the first Treaty of Viterbo with William II of Achaea, who swore fealty and recognised the Angevin dynasty as his successor. The exiled emperor Baldwin II reaffirmed the agreement in return for Charles's promise to recover Constantinople. Charles thus assumed leadership of anti-Byzantine crusading initiated by Pope Urban IV, though Urban's successor, Clement IV did not grant indulgences for the expedition.^[245][246]

The church union, however, proved deeply unpopular, as hostility towards Westerners persisted after the Sack of Constantinople. Opposition arose from monks, courtiers, and even Michael's sister Eulogia. His failure to implement the union angered the papacy, and in 1281 Pope Martin IV excommunicated him and authorised Charles to launch an anti-Byzantine crusade.^[247] Michael responded by encouraging opposition to Charles and Venice, contributing to the War of the Sicilian Vespers between Charles and Aragon, which brought Charles's ambitions to an end.^[248] After Michael's death in December 1282, his son and successor Andronikos II Palaiologos repudiated the union.^[249]

The War of the Sicilian Vespers hindered new crusades for the Holy Land, allowing the Mamluks to complete the conquest of the Crusader states by 1291. Preoccupied with internal conflicts, the Byzantines paid little attention. Western crusade theorists, however, continued to refer to Byzantium: Pierre Dubois proposed conquering Constantinople, while Ramon Llull preferred peaceful cooperation.^[250] Plans for anti-Byzantine crusading mainly envisaged a limited passagium particulare: a relatively small, tax-financed mercenary force, premised on the conviction that possession of Constantinople was vital to the recovery of the Holy Land. More mundane motives, notably power politics and commercial interests, also played a significant role.^[251]

Emperor Michael VIII Palaiologos focused on defending European territories, neglecting Anatolia. His son and successor Andronikos II attempted to resist Turkoman advances but was defeated by Osman I, founder of the Ottoman state, at the Battle of Bapheus in 1302.^[252][248] In the west, Andronikos sought alliances with Ghibelline (anti-papal) powers, marrying Yolande, daughter of the Ghibelline leader William VII of Montferrat. He also pursued a marriage between his son Michael IX and the titular Latin empress Catherine of Courtenay, but this failed.^[253][254] Catherine instead married Charles of Valois, brother of Philip IV of France, whose campaigns elsewhere prevented him from asserting her claim to Constantinople.^[255]

In 1302, the Peace of Caltabellotta ended the War of the Sicilian Vespers, leaving the Catalan Company—a mercenary group—unemployed. Andronikos II hired c. 6,500 Catalans to fight the Turkomans, promising 1,200,000 hyperpyra, exceeding the empire's annual revenue. When payment failed, the Catalans revolted, enabling Genoese expansion in the Aegean, Turkoman gains in Anatolia, and Bulgarian advances into Thrace.^[256] Charles of Valois exploited the crisis, allying with Venice and persuading Pope Clement V to proclaim an anti-Byzantine crusade, but he failed to raise the crusade taxes. His plans collapsed, and Venice reconciled with Byzantium in 1310.^[257]

In 1313, Philip I of Taranto, holder of the Angevin claim to suzerainty over Achaea, married Catherine of Valois, heir to the titular empress Catherine I. Pope Clement supported Philip's plans for an anti-Byzantine campaign by granting crusade indulgences and tax funds. However, Philip's commitments in Italy and Greece drained his resources, and he abandoned plans to attack Byzantium in 1320.^[258][257] By then, crusading theorists' interest in reconquering Constantinople had waned, and anti-Byzantine crusading effectively faded.^[257]

Emperor Andronikos II's attempt to disinherit his grandson, the younger Andronikos, following the murder of his brother Manuel, triggered a civil war in 1321 in which the younger Andronikos was proclaimed emperor. The conflict invited Serbian and Bulgarian incursions and facilitated Ottoman advances in Anatolia.^[259] The elder Andronikos' efforts to secure western support failed amid strong anti-Latin sentiment, despite the backing of the crusading theorist Marino Sanudo Torsello.^[260]

The younger Andronikos became sole emperor after his grandfather's abdication in 1328.^[261] By then, Anatolia had fragmented into beyliks, autonomous Turkoman lordships that recruited ghazi warriors to wage jihad. As some developed fleets threatening merchant shipping, a naval league was formed at Venice's initiative under the auspices of Pope John XXII, who defined its aims as an opus fidei ('work of faith').^[262][263] Andronikos III promised ten ships, but soon agreed to pay an annual tribute of 20,000 hyperpyra to the Ottoman ruler Orhan. He also maintained friendly relations with Umur, ruler of the maritime Aydinid beylik. Although Andronikos eventually withdrew from the league, its forces defeated the Karasids' fleet at the Battle of Adramyttion in 1334, but failed to eliminate the beyliks' naval threat.^{[264][265][266]}

With most remaining Anatolian territories lost to the Turkomans, Andronikos reoriented imperial policy westwards.^[267] Several Frankish lords were willing to acknowledge his overlordship, yet his sudden death in 1341 left his nine-year-old son, John V Palaiologos, as emperor. Although he had appointed his friend John Kantakouzenos as regent, Kantakouzenos's absence enabled the Dowager Empress Anna to establish a rival regency, prompting him to proclaim himself co-emperor as John VI. The ensuing civil war allowed the Serbian ruler Stefan Dušan to seize Macedonia and Thessaly, while Turkoman forces ravaged Thrace and Thessalonica fell under the autonomous Zealot regime. In 1347 the Black Death reached the empire, killing roughly one third of its population. Amid these crises, John VI renewed negotiations on church union and proposed joining a new crusade against Umur, even as he continued to seek support from both Umur and Orhan. In March 1354, following a devastating earthquake, the Ottoman Turks captured Gallipoli, securing their first foothold in Europe. Kantakouzenos's pro-Ottoman stance eroded his popularity, allowing John V to assume full control of the government.^[268]

The Ottoman occupation of Gallipoli enabled the ghazis to cross into Europe with ease, prompting John V to seek western support. He proposed a two-stage crusade, in which an initial limited passagium would demonstrate to the Byzantines both the effectiveness of western aid and the necessity of church union. Pope Innocent VI duly proclaimed a new crusade, preached in Italy and Frankish Greece, and appointed Bishop Peter Thomas as legate. Accompanied by Venetian and Hospitaller galleys, the legate and Byzantine forces attacked the Ottoman stronghold of Lampsacus in Anatolia, but the focus of crusading efforts soon shifted to the southern Mediterranean, where Peter I of Cyprus revived plans for a campaign to recover the Holy Land.^[269]

Ottoman expansion continued under Orhan's son, Murad I, who captured Philippopolis in 1363. Pope Urban V appealed to several Catholic powers, including Louis I of Hungary and Amadeus VI of Savoy, urging them to take up arms in support of Byzantium. In 1366, John V met Louis at Buda, in what was the first recorded state visit of a Byzantine emperor to a foreign court, but it proved unsuccessful. On his return, he was detained by Ivan Alexander of Bulgaria at Vidin.^[270] Meanwhile, Amadeus, John's maternal cousin, en route from Italy to join the crusade of Peter I, was diverted by the Venetians and seized Bulgarian ports on the Black Sea coast, thereby securing John's release.^[271] In 1369, the Ottomans captured Adrianople, prompting John to travel to Rome, where he formally submitted himself to the papacy; on his return to Constantinople, however, he was held by the Venetians until his debts were settled in 1371. In the same year, Murad inflicted a crushing defeat on a coalition of Serb princes at the Battle of Maritsa, compelling John to accept his suzerainty.^[272]

Fearing of an Ottoman invasion of Frankish Greece or Italy, Pope Gregory XI tried to organise a large conference of western powers at Thebes to plan a new crusade, but his attempt failed, and a new war between Genoa and Venice prevented their cooperation against the Ottomans. The Ottomans captured Thessaloniki in 1387, and defeated a coalition of Serbian and Bosnian rulers at the Battle of Kossovo in 1389, although Murad was killed during the battle.^[273]