Conflict between the Germanic tribes and the forces of Rome under Julius Caesar forced major Germanic tribes to retreat to the east bank of the Rhine. Roman emperor Augustus in 12 BC ordered the conquest of the Germans, but the catastrophic Roman defeat at the Battle of the Teutoburg Forest resulted in the Roman Empire abandoning its plans to completely conquer Germany. Germanic peoples in Roman territory were culturally Romanized, and although much of Germany remained free of direct Roman rule, Rome deeply influenced the development of German society, especially the adoption of Christianity by the Germans who obtained it from the Romans. In Roman-held territories with Germanic populations, the Germanic and Roman peoples intermarried, and Roman, Germanic, and Christian traditions intermingled. The adoption of Christianity would later become a major influence in the development of a common German identity.

What emperor forced the Germanic tribes to the east side of the Rhine?