There were portrayals of seven Ecumenical Councils in the central part of St. Sophia Cathedral. Only the portrayal of the First Ecumenical Council has been preserved. The First Ecumenical Council took place in 325 in Nicaea (present-day Iznik, Turkey). Therefore, it is also called the First Council of Nicaea. The basic doctrines of Christianity were defined and approved at this Council. The Council was convened by the Emperor Constantine the Great.