That trend would, of course, later lead to tensions between the church centered in Constantinople and the one centered in Rome, but more on that in a bit. To give you a sense of how dramatic this shift was, by the 4th century CE, Constantinople's population had soared, while Rome's had gone from 500,000 to 80,000. And although the Byzantines spoke Greek, not Latin, they considered themselves Romans, and if they did, we probably should too. Let's go to the Thought Bubble. There was a lot of continuity between the old Western Roman Empire and the new Eastern one. Politically, each was ruled by a single man, sometimes there were two and once there were four, but let's forget about that for now, who wielded absolute military power. War was pretty much constant as the Byzantines fought the Persian-Sasanian Empire and then various Islamic empires.