The event that initiated the Great Schism between the Eastern Orthodox and Roman Catholic Churches was the mutual excommunication in 1054. Tensions had been escalating for centuries, primarily over issues such as theological disagreements, church leadership, and liturgical practices. The final break occurred when the Pope and the Patriarch of Constantinople excommunicated each other, solidifying the division between Western Christianity, under the authority of the Pope in Rome, and Eastern Christianity, centered in Constantinople. This schism profoundly shaped the religious landscape of Europe and has enduring effects on Christian relations to this day.