In pre-Roman times the territory now known as Switzerland was inhabited by the Helvetii in the west and the Rhaetians, a people believed to have been related to the Etruscans, in the east. In the 1st century bc Julius Caesar and the Romans conquered the region, which they named Helvetia, and it became thoroughly Romanized. A series of Germanic invasions swept over the Western Roman Empire in the 4th century ad, and two Germanic groups—the Burgundians and the Alamanni—conquered Helvetia.