Preface to Constantine: The Rule of the Four

In this post I want to explain how Constantine came to power. It is an unusually complicated story, with all kinds of names and dates that only inveterate historians could love. I’ll give a simple version of it here, more suitable for those of us who are mere mortals.

The reason it matters is that Constantine’s predecessor’s Diocletian vision of a Tetrarchy (= Rule of Four), in which the empire would be ruled by two senior emperor (each called an Augustus) and two junior emperors (each called...