The Council of Chalcedon ( or ) was a church council held from October 8 to November 1, AD 451, at Chalcedon (a city of Bithynia in Asia Minor), on the Asian side of the Bosphorus, known in modern times as Kadiköy in Istanbul Province of Republic of Turkey, although it was then separate from Constantinople. The judgements and definitions of divine nature issued by the council marked a significant turning point in the Christological debates that led to the separate establishment of the church in the Western Roman Empire during the 5th century.