When people refer to ancient empires these days, especially the biggest ones, Rome is invariably brought up. The fall of the Roman Empire is used as an example of greatness toppled by its own avarice, pride, greed, foolishness, or whatever other vice is being explained. The thing is, while the Roman Empire did conquer vast expanses of the world and it did exist for a very long time, in a technical sense it was not actually that big. Relatively speaking, at under two million square miles, the…