The Germanic invasions of the Western Roman Empire did not happen all of a sudden. Just as the Han people living on the Central Plains called the neighboring tribes as “Yi” and “Di” (夷狄), the Romans used “the barbarians” to call the great variety of groups living beyond the Rhine and the Danube rivers (later they were called “the Germans”). Just like the Han people’s relations with their neighboring tribes, the Romans’ relations with the Germans fluctuated from wars to alliances. Just like the Han court, which tried – not always successfully – to protect itself behind the Great Wall, the Romans came to rely on Limes Germanicus (Germanic Frontier), a series of fortifications along the Rhine and the Danube. And just as the Central Plains came to be controlled by the Northerners, the Western Roman Empire was overrun by the Germanic tribes.