I just completed a quite excellent biography of the Emperor Diocletian, “Diocletian and the Military Restoration of Rome” by Lee Fratantuono. The author tells the story of what had to have been, adjusted for circumstances, one of the most successful emperors in Roman history. 

After the crisis of the 3rd Century, with the empire constantly torn between domestic upheaval, civil war, and foreign invasion, a military commander who was of lowly birth (either a freed slave or a descendant of ...