I'm looking for something that outlines his reforms to the Roman military. I heard on a podcast that he instigated a heavier emphasis on flying columns and cavalry to combat the hit and run tactics on the frontiers, but I can't find more than that. I've got a nice hardback on the Roman military but it's quiet when it gets to Diocletian, and mentions him very little. If his reforms weren't as substantial as I'm giving him credit for, then what did the army look like that he commanded? How did he use it in a pitched battle versus skirmishes and raiding, and did it translate well into sieges (I'm thinking Alexandria though there may have been more)? Sorry for the loaded question, but any literature on the subject would be greatly appreciated.
For a look at Diocletian ' s reforms I would direct you to the works of Adrian Goldsworthy, primarily "The Complete Roman Army" and "How Rome Fell".
Basically Diocletian is not credited with individual army tactics but rather with the fundamental restructuring of the Roman army into border and reserve units.
Border armies were smaller, with more mixed troops and cavalry. They dealt in speedy and stealthy attacks to secure the frontiers against small scale forces. If a larger army came by they would retreat to their forts and await the larger field forces.
The field armies had the more standard assortment of heavy infantry. These armies were billeted in cities to decrease the stress of their upkeep. They were meant to help provide for internal security against usurpers and as a force which could be shifted to areas in need.