May 5 — Galerius issues his Edict of Toleration, ending persecution of Christians in his part of the Roman Empire.
Maxentius reconquers the African provinces from Domitius Alexander.
Maximinus and Licinius share the Eastern Empire.
Maximinus recommences the persecution of Christians.
Asia
Luoyang, the Jin Dynasty (265-420) capital of China, is sacked by groups of barbarians under the leadership of Huns. Jin Huai Di, emperor of China, is captured.
By Topic
Religion
July 2 — Pope Miltiades succeeds Pope Eusebius as the 32nd pope.
The Donatist schism occurs in the African church.
On his deathbed, Galerius declares religious freedom throughout the Empire, focusing on ending anti-Christian persecution.
Deaths
May 5 — Galerius, Roman emperor
November 25 — Peter, Patriarch of Alexandria (martyred)