Excerpts from Books and Wikipedia
"In all, he issued four edicts against Christians--the first, in February 303, called for the destruction of all churches throughout the Roman Empire; the last, published in April 304, ordered all Christians to sacrifice to the traditional gods of Rome of face execution. At this time, probably about 10 percent of the population professed Christianity. . . . Realizing it was too big for one man to govern, he had established the Tetrarchy (rule by four), by which he ruled as emperor (Augustus) in the east with Galerius as his caesar, and Maximian ruled as Augustus in the west with Constantius as his caesar. In 305, Diocletian, by now in poor health, took the extraordinary step of abdication, retiring to the magnificent palace he had built for himself at Split on the Adriatic coast." [1001 Days]