or Rhaetia
Ancient Roman province south of the Danube River .
It comprised parts of present-day Austria, Switzerland, and Germany. Its native inhabitants were probably of mixed Illyrian and Celtic descent. Conquered by Rome in 15 BC, it became an important part of the empire for its position on the highways between Italy and the Danube and between Gaul and the Balkans. Because it was a frontier province, its boundaries shifted when German tribes encroached; in the 1st century AD, the northern boundary extended to the Neckar River , but in the 3rd century the western and northern boundaries were pulled back. By 450, Rome controlled only the alpine regions.