Norman expansion in southern Italy and Sicily disrupted long-standing zones of Greek (Byzantine-rite) Christianity and intensified jurisdictional competition between Rome and Constantinople—an important political backdrop to later ecclesiastical ruptures.
Patriarch Michael I Keroularios (Cerularius) moved against Latin-rite practice in Constantinople, including the closure of Latin churches, escalating a conflict already inflamed by disputes over liturgy and papal claims.
Pope Leo IX dispatched legates led by Cardinal Humbert to negotiate with the Byzantine court and patriarchate amid disputes over authority and rite; the mission deteriorated rapidly amid mutual hostility.
During the Divine Liturgy, Cardinal Humbert and fellow legates placed a bull of excommunication targeting Patriarch Michael I and associates on the altar of Hagia Sophia—an emblematic moment of the 1054 rupture.
A synod in Constantinople responded by anathematizing Humbert and his colleagues (rather than issuing a blanket condemnation of the entire Western Church), hardening the breach in practice.
A synod at Blachernae Palace (under Alexios I Komnenos) dealt with controversy over the imperial use of church wealth and sacred objects for state needs—illustrating the intense entanglement of Byzantine politics and church authority on the eve of deeper Latin-Greek estrangement.
At Piacenza, Pope Urban II received envoys linked to Emperor Alexios I Komnenos requesting aid against the Turks—an opening for renewed East–West coordination that would soon transform into crusading movement with complex ecclesiastical consequences.
Urban II convened the Council of Clermont and called for armed assistance to Christians in the East and for the expedition to the Holy Land. Although connected to Byzantine requests, the crusade reshaped Byzantine–Latin relations and introduced new points of friction over authority and territory.
Pope Urban II presided over the Council of Bari, where disputes such as the Filioque and Eucharistic practices were discussed in a setting that included bishops identified as Greek/Orthodox—highlighting continued, contested efforts to define Latin and Greek orthodoxy after 1054.
Following conflict with Bohemond of Antioch, the Treaty of Devol sought to make Antioch a Byzantine vassal and included provisions touching church leadership (e.g., a Greek patriarch). The treaty’s contested implementation reflected enduring Byzantine distrust of Latin intentions after the First Crusade.
During the Fourth Crusade, Latin forces captured Constantinople (April 1204) and subjected it to extensive sack and looting. The conquest shattered Byzantine political and ecclesiastical structures in the capital and represented a major rupture in Byzantine–Latin religious relations.
In the aftermath of 1204, Venetian-backed clergy elected Thomas Morosini as the first Latin Patriarch of Constantinople. His contested election and policies reflected the difficulty of legitimizing Latin ecclesiastical authority over an overwhelmingly Orthodox population.
After the conquest, crusader leaders established the Latin Empire; Baldwin of Flanders was elected (and soon crowned) as its first emperor, signaling a durable political-religious realignment that marginalized the Orthodox hierarchy in the city.
A partition agreement (often referred to as the Partitio of the former Byzantine Empire) arranged the distribution of Constantinople and imperial territories between Venice, the new Latin emperor, and other crusader leaders—binding conquest to new Latin ecclesiastical and political claims.
The Great Schism and Byzantine–Latin Ecclesiastical Relations (1000–1204)
