In church history, the Nestorian Schism of 431AD to 544AD involved a split between the Christian churches of Sassanid Persia, which affiliated with Nestorius, and churches that rejected him. The schism rose out of a Christological dispute, notably involving  Cyril (Patriarch of Alexandria) and Nestorius (Patriarch of Constantinople). The First Council of Ephesus in 431 and the Council of Chalcedon in 451 condemned Nestorius and the doctrine he was accused of, which emphasized the distinctness between  Christ's human and divine natures. This forced a breach between those Churches which defended Nestorius and the state church of the Roman Empire, thereby causing the Church of the East - the Christian church of Sassanid Persia - to become known as the Nestorian Church for taking the side of Nestorius. Despite ratifying the Council of Chalcedon at the 544 Synod of Mar Aba I, the Christians of the Church of the East have been known most commonly - though inaccurately - as the Nestorians ever since.