Patriarchate and the Chalcedonian Schism
The Council of Chalcedon (451) affirmed that Christ is acknowledged in two natures, divine and human, united without confusion and without division, in opposition to the teaching of Eutyches. The same council deposed Dioscorus of Alexandria, and Proterius, a priest of the city known for his opposition to the Monophysite position, was placed on the patriarchal throne.
The Egyptian church was largely unwilling to accept the Chalcedonian definition, and Proterius governed amid sustained hostility. The historical record reports that his arrival in Alexandria was met by a riot, and his tenure is regarded as the opening of the schism between the Chalcedonian and anti-Chalcedonian communities of Alexandria.