One major factor probably was the Huns that caused this great migration in the fourth and fifth centuries that caused the Germanic tribes to cross the Rhine and cross the Danube and become either, or either settle as part of the Roman Empire or threaten the Roman Empire. Another theory, and all of these are probably contributors, is that as the Germanic tribes settled, they actually became more and more part of the Roman military. And some of them were officially part of the military. Some of them were mercenaries, soldiers for fortune, paid soldiers. And so you can imagine their allegiance to Rome was not as strong. Some folks say Christianity may have been a factor, that the empire might have lasted, especially when people were doing what their traditional rites, rituals, they worshiped an emperor, but now Christianity wasn't about worshiping an emperor anymore. A lot of people think it's corruption, instability, and we've talked a little bit about that.