Large Map of Roman Empire
under Emperors Diocletian and Constantine

Diocletian
Lived from c. 245 to c. 312 A.D.
Roman Emperor from November 20, 284 to May 1, 305 A.D.

Constantine
(also known as Constantine I or Constantine the Great)
Lived from February 27, 272 to May 22, 337 A.D.
Roman Emperor from 306 to 337 A.D.

Constantine is remembered for the Edict of Milan in 313 A.D.
which for the first time in the Roman empire gave imperial favor to Christianity.