Centuries: 3rd century - 4th century - 5th century
- February 6 - Julius is elected pope.
- June 17 - Constantius II announces the restoration of Athanasius to the Patriarch of Alexandria.
- September 9 - Constantine II, Constantius II, and Constans succeed their father Constantine the Great as co-emperors of the Roman Empire.
- A number of descendants of Constantius I Chlorus, as well as powerful nobles, are executed. Responsibility for this purge is denied by the three Augusti.
- November 25 - Athanasius enters Alexandria.
- Paul I becomes Patriarch of Constantinople.
- Shapur II of Persia begins a war with the Roman Empire.
- May 22 - Constantine I, Roman emperor
- September - Hannibalianus, King of the Pontus and grandson of Constantine I (executed)
- September - Dalmatius, Caesar and grandson of Constantine I (executed)
- September - Julius Constantius, son of Constantius I Chlorus and father of Julian (executed)
- September - Patricius Optatus (executed)
- September - Ablavius, Prefect of the Imperial Guard (executed)
- Eustathius, Patriarch of Antioch (probable date)
- Alexander, Patriarch of Constantinople\n