Diocletian (/ Ë d aÉª. É Ë k l iË Ê Én /; Latin: Gaius Aurelius Valerius Diocletianus Augustus), born Diocles (244â312), was a Roman emperor from 284 to 305. Born to a family of low status in Dalmatia, Diocletian rose through the ranks of the military to become Roman cavalry commander to the Emperor Carus. After the deaths of Carus and his son Numerian on campaign in Persia, Diocletian was proclaimed emperor.