Diocletian was one of the most effective emperors of the changing Roman empire. He is probably best known for his halt of the 3rd century chaos that overwhelmed the empire. He also established the short lived government rule of a tetrarchy. The tetrarchy distributed power equally among four co-rulers in four frontier cities of the empire. Specifically these were Nicomedia, Mediolanum, Antioch and Trier. More notably it took the leadership role from the decaying city of Rome and paved the way for the new capital of Constantinople in the eastern empire. He took as his co-rulers Maximian, his fellow officer, as co-emperor (in 286 AD) and as junior co-emperors Galerius and Constantius (in 293 AD). Diocletian also made the Roman empire the most bureaucratic in its existence. He did this by expanding civil and military services, as well as placing more emphasis on distribution of power in the newly formed administrative districts. Diocletian was the first Roman emperor to step down from power. He retired to the Dalmatian coast and died a natural death as compared to the rulers before who usually met their fate via battle or assassination.

Unfortunately Diocletian was also known for his horrific treatment of Catholics. From 303-311 AD, he was responsible for the persecution and murder of scores of people. This only ended with the accession of Constantine I, the Great, who was a Catholic. More damaging to his legacy, the tetrarchy suffered a collapse shortly after Diocletian had retired. 

Coinage of Diocletian from Alexandria is abundant. Some of this can be explained that during the tetrarchy he was responsible for Egypt.