At the time of Chalcedon the Alexandrian Patriarchate included around one hundred bishops in it's synod, with scholarly estimates ranging from ninety to a hundred and eight bishops. Pope Dioscorus of Alexandria was accompanied to Chalcedon by nineteen bishops. During the first session of Chalcedon, four of these bishops, (Athanasius of Busiris (or of Perulis / Tripolis), Auxonius of Sebennytus, Nestorius of Phlabonis and Macarius of Cabasa), crossed the floor from the right side (where the Egyptian delegation originally sat with Dioscorus) to the left side with his opponents, publicly expressing approval of the orthodox standing of the deposed Flavian of Constantinople. "All four bishoprics were located in the province of Aegyptus II. Perhaps a regional issue had triggered episcopal resentment against the patriarch, or perhaps their desertion was simply a prudent political decision by four companioned bishops who would benefit and go on to play a major role for the Egyptian Church in the immediate aftermath of the Council of Chalcedon." (Volker-Menze, The Last Pharaoh, pg. 72-73)
"In the fourth session, thirteen Egyptian bishops put up remarkable resistance
against all other bishops in attendance, who forcefully urged them to condemn
Dioscorus and accept the Tome of Leo. These thirteen bishops, led by Hieracis
of Aphaeum, who had already accompanied Cyril to the Council of Ephesus
twenty years earlier, emphasized procedural reasons for their resistance: they
would only obey a newly elected patriarch of Alexandria. As the council insisted,
though, the Egyptian bishops threw themselves on the ground and begged for
mercy (Acts of Chalcedon IV.49), claiming that they feared for their life if they
were to anathematize Dioscorus and agree to the Council of Chalcedon. If the
council would not consent to their petition, they preferred to die now rather than
to submit to the council and be killed at home. It is unimaginable that the
Egyptian bishops would humiliate themselves in such a way if there were any
sizeable opposition among the Egyptian episcopate. Dioscorus must have been
respected if not popular in Egypt, and the bishops feared the reactions of their
communities if they deserted him.
Two Egyptian bishops neither deserted Dioscorus nor even attended the
fourth session: Theodulus of Tesila and Isaias of Hermopolis Minor. They had
been firm supporters of Dioscorus’ ecclesiastical politics previously. Theodulus’
verdict in Ephesus in 449 is recorded thusly: ‘It would have been better for the
former bishops Flavian and Eusebius if they had not been born, but to have
millstones hung round their necks and be thrown into the sea.’ Considering
the aggressive language (based on Mt 26:24 and Mt 18:6), Theodulus—and
perhaps also Isaias—might have belonged to a radical faction in Egypt that,
after the first session of Chalcedon, believed that any doctrinal hope was lost,
and therefore they were not even willing to defend their position in front of
the other bishops in the fourth session. In short, four bishops deserted
Dioscorus when it became obvious that his case had been lost, thirteen defended
him publicly, and two others might have been in radical opposition to the
Chalcedonian bishops." (Volker-Menze, The Last Pharaoh, pg. 72)
The four deserting bishops, "ordained Dioscorus’ successor, Proterius, and Nestorius became the new patriarch’s right-hand man, serving him on a mission to receive papal approval of Proterius’ election." (Volker-Menze, The Last Pharaoh, pg. 73) Proterius had been appointed by Dioscorus as archpriest (or chief steward/presbyter) of the Church of Alexandria. Since it takes twelve bishops to ordain a patriarch, eight foreign bishops travelled to Egypt and aided the four Egyptian bishops, with his consecration.