Diocletian’s persecution was the tenth decreed persecution under the emperors of Rome (303-313 AD). (The Fifth Seal, 303-313 AD, pg. 33).
“In 303 Diocletian issued in rapid succession three edicts, each more severe than its predecessor. Maximian [his co-regent] issued the fourth, the worst of all, April 30, 304. Christian churches were to be destroyed; all copies of the Bible were to be burned; all Christians were to be deprived of public office and civil rights; and at last all, without exception, were to sacrifice to the gods upon pain of death.”
Philip Schaff, History of the Christian Church, Vol. 2, p. 68.