Daily History Challenge · No. 47 · Friday 14 August 2026 · When?
Puzzle No. 47: When?
The event was Council of Chalcedon and the First Permanent Christian Schism, in 8 October to 1 November 451 CE.
The answer
The Council of Chalcedon, the fourth ecumenical council, convened from 8 October to 1 November 451 at Chalcedon in Bithynia (modern Kadikoy, Istanbul), summoned by the Eastern Roman emperor Marcian and attended by roughly 520 bishops, the largest gathering of the early councils. To resolve the dispute over how Christ could be both fully divine and fully human, the council adopted the Chalcedonian Definition, drawing on Pope Leo I's Tome, declaring that Christ exists in two natures 'without confusion, without change, without division, without separation.' It condemned and deposed Dioscorus, patriarch of Alexandria, and rejected the Monophysite teaching associated with the monk Eutyches. Many churches in Egypt, Syria, Armenia, and Palestine refused to accept the two-nature formula, regarding it as a betrayal of Cyril of Alexandria's Christology, which precipitated the first permanent schism in Christianity. This split produced the non-Chalcedonian (Oriental Orthodox) churches, including the Coptic, Syriac, Armenian, and Ethiopian communities, a division that remains unhealed to this day and weakened Byzantine control of its eastern provinces.