[SeeSharp]

The Romans ventured across the Rhine briefly, before being repulsed.

The Romans maintained that border for 400 years. They traded across it and raided across it for the entire period. There were tens of thousands of German slaves in the Roman empire throughout the entire period.

Who sacked Rome?

The Visigoths - four hundred years after Rome's first contact with the Cimbri (German/Scandinavian/???).

[IronJack]

Julius Caesar reached the Rhine in around 60 BC. His troops crossed the river, as did a handful of other commanders, including Varus, but after the latter's defeat at Teutoburg (9 AD), the Romans abandoned the idea of conquering the East.

They settled in parts of the South but the Northern Rhine remained the northernmost boundary of the Empire until well into the fifth century. And as early as the third century, the Alamanni -- early Germans -- kicked the intruders out of the Black Forest region.