|Centuries:||3rd century – 4th century – 5th century|
|Decades:||290s 300s 310s – 320s – 330s 340s 350s|
|Years:||321 322 323 – 324 – 325 326 327|
- July 3 – Battle of Adrianople: Emperor Constantine the Great defeats his rival Licinius near Adrianople. They retreat to Byzantium. He invades Thrace with a Visgothic force and raids the countryside.
- July – Battle of Hellespont: Crispus, destroys Licinius' naval fleet in the Dardanelles.
- September 18 – Battle of Chrysopolis: Constantine I defeats Licinius at Chrysopolis. He becomes sole Emperor.
- December 19 – Licinius gives up his position as Emperor.