Centuries: 3rd century - 4th century - 5th century
- First Council of Constantinople - second Ecumenical council of the Christian Church: The Nicene creed is affirmed and extended, Apollinarism is declared a heresy.
- Council of Aquilea: under the guidance of Ambrose, the chief Arianist bishops Palladius and Secundadius are deposed.
- Flavian succeeds Meletius as Patriarch of Antioch.
- Timothy succeeds Peter as Patriarch of Alexandria.
- A deputation from the Roman Senate delivers to Gratianus the robe of the Pontifex Maximus, which had been worn by every Roman Emperor since Augustus. He refuses to accept this insignia, insulting the pagan aristocrats of Rome.
- Nectarius succeeds Gregory Nazianzus as Patriarch of Constantinople.
- John Chrysostom becomes a deacon.