Loyola University Chicago
De Imperatoribus Romanis: Diocletian
This is a biographical history of Diocletian and the Rome of his time. Includes links to other Roman subjects.
Then Again
Then Again: Web Chron: The Emperor Diocletian
Article provides a description of the life and rule of the Emperor Diocletian.
Forum Romanum
Outlines of Roman History: Reorganization of Empire: The Reign of Diocletian
The reign of Diocletian is discussed in this article from William Morey's 1901 textbook. Check out the chart that shows how the Roman Empire was split into East and West.
Other
Willamette Coin Club: The Times and Coinage of Diocletian: 284 305 a.d.
A description of the massive job facing Diocletian when he assumed the leadership of the Roman Empire, and how he developed the tetrarchy. There is also information about Roman coinage.