During the Gallic War, Julius Caesar ended the Germanic control of Alsace by defeating Ariovistus. He built a bridge across the Rhine in 55 BC and entered Germania. He convinced the Suebi and other tribes not to interfere in Gaul, which was Roman territory. Other than venturing into Germania a second time in 53 BC and warring against several tribes, he left Germania alone. This established the Rhine as the boundary between Germania and Roman Gaul. 