What nomads? With the possible exception of the semi-nomadic Celtic peoples I can't think of a single European nomadic group the Romans encountered and settled--and the Celts don't really count at all, because by the time of Roman contact they were most certainly a settled people, whether they be Gauls, Galatians, or Britons. He must be confusing migratory groups like the Teutones with actual nomads--but groups migrating from one place to another are not in any way nomadic, they're leaving their old homelands and moving to new ones for whatever reason. The Romans settled plenty of these people, particularly towards the end of the western imperial period, but they're about as nomadic ad refugees--indeed, one could think of migratory populations as being a sort of refugee population. What nomadic populations could he possibly be thinking about, does he give any examples or does he just drop this statement about magical European nomadic groups? The Scythians and Sarmatians are the only true nomads I can think of that the Romans encountered in large numbers, and they were never fully subjugated, though many Sarmatians were settled in Thrace and elsewhere