- May 26 The Battle of Avarayr between Armenian rebels and the Sassanid Empire takes place. The Armenians are defeated militarily but are guaranteed freedom to openly practice Christianity.
- Jun 20 Battle of the Catalaunian Plains: Roman and Visigoths forces defeat Attila the Hun in north east France, alting Hun invasion of Roman Gaul (exact date disputed)
- Jun 24 10th recorded perihelion passage of Halley's Comet
- Oct 8 Council of Chalcedon (4th ecumenical council) opens - acts of second Council of Ephesus annulled and doctrine of Pope Leo's Tome adopted