321 322 323 324 – 325 – 326 327 328 329
| Decades: |
290s 300s 310s – 320s – 330s 340s 350s
| Centuries: |
3rd century – 4th century – 5th century
- May 20 – First Council of Nicaea – first "Ecumenical Council" of the Christian Church: The Nicene Creed is formulated, the date of Easter is discussed.
- Gladiatorial combat is outlawed in the Roman Empire.
- The Church of the Nativity is built in Bethlehem
- Jin Cheng Di succeeds Jin Ming Di as emperor of China.
- Procopius, attempted usurper of the Roman Empire (approximate date)
- Ammianus Marcellinus, Roman historian (approximate date)