Centuries: 3rd century - 4th century - 5th century
- July 25 - Constantine I proclaimed Roman emperor by his troops.
- October 28 - Maxentius, son of the former Roman emperor Maximian proclaimed emperor.
- Flavius Valerius Severus is proclaimed Augustus.
- The Council of Elvira declares killing through a spell a sin and the work of the devil.
- Santa Maria Maior de Lisboa is built in Lisbon.
- The Tomb of Galerius is built in Thessaloniki.
- The War of the Eight Princes ends in China.
- Saint Metrophanes becomes bishop of Byzantium.