The Council of Chalcedon (/kælˈsiːdən/ or /ˈkælsᵻdɒn/) was a church council held from October 8 to November 1, AD 451, at Chalcedon. The Council is considered to have been the fourth ecumenical council by the Great Church. Not all Christians agreed with its teachings. Its most important achievement was to issue the Chalcedonian Definition. The Council's judgements and definitions regarding the divine marked a significant turning point in the Christological debates. Chalcedon was city of Bithynia in Asia Minor, on the Asian side of the Bosphorus; in modern times it is known as Kadıköy and is part of Istanbul Province in the Republic of Turkey.