St Cyril was the nephew of Patriarch Theophilus of Alexandria, who educated him from his youth. He succeeded to his uncle’s position in 412, but was deposed through the intrigues of the Nestorian heretics. He later resumed his See, however.
St Cyril presided at the Third Ecumenical Council in 431, which censured the Nestorian blasphemy against the Most Holy Theotokos. His wise words demonstrated the error of their false doctrine.
St Cyril departed to the Lord in the year 444, and is also commemorated on June 9 (the day of his repose).
Troparion — Tone 3
You shone forth with works of Orthodoxy and quenched all heresy, / and became victorious trophy-bearers, hierarchs Athanasius and Cyril. / You enriched all things with piety and greatly adorned the Church, / and worthily found Christ God, / who grants His great mercy to all.
Kontakion — Tone 4
Athanasius and Cyril, great hierarchs of true piety, and noble champions of the Church of Christ, / preserve all who sing: / “O Compassionate Lord, save those who honor You.”