Definition: The Emperor Marcian convened the fourth ecumenical council, the Council of Chalcedon, on October 8, 451. Estimates of the number of bishops in attendance at the Council of Chalcedon range from 500 to 600. The doctrinal formula accepted by the council, which had been convened in response partly to the challenge of the Monophysites was that Christ is one in two natures (human and divine). A definition of the faith was adopted at the Council of Chalcedon. There were also 29 canons ratified by Pope Leo I.