He was ordained priest by St. Cyril, but opposed Dioscorus, his successor, on his patronizing Eutyches, and giving into his errors, notwithstanding his endeavor to gain him to his interest, by making him archpriest, and entrusting him with the care of his church. Dioscorus being condemned and deposed by the council of Chalcedon, Proterius was elected in his room, and was accordingly ordained and installed in 552. The people of Alexandria, famed for riots and tumults, then divided; some demanding the return of Dioscorus, others supporting Proterius. The factious party was headed by two vicious ecclesiastics, Timothy, surnamed Elurus, and Peter Mongus, whom the saint had canonically excommunicated. And so great and frequent were the tumults and seditions they raised against him, that during the whole course of his pontificate he was never out of danger of falling a sacrifice to the schismatical party, regardless both of the imperial orders and decisions of the council of Chalcedon.
In the height of one of these tumults, Elurus, having caused himself to be ordained by two bishops of his faction, that had been formerly deposed, took possession of the episcopal throne, and was proclaimed by his party the sole lawful bishop of Alexandria. But being soon after driven out of the city by the imperial commander, this so inflamed the Eutychian party, that their barefaced attempts obliged the holy patriarch to take sanctuary in the baptistery adjoining to the church of St. Qnirinus, where the schismatical rabble breaking in, they stabbed him on Good-Friday, in the year 557. Not content with this, they dragged his dead body through the whole city, cut it in pieces, burnt it and scattered the ashes in the air. The bishops of Thrace, in a letter to the emperor Leo, soon after his death, declared that they placed him among the martyrs, and hoped to find mercy through his intercession. Sanctissi mum Proterium in ordine et choro sanctorum martyrum ponimus, et ejus in. tercessionibus misericordem et propitium Deum nobis fieri postulamus.
(Source: Butler’s Lives of the Saints)