Final answer:
The Romans called upon the 'barbarians' for help with labor shortages, with the most notable group being the Visigoths, a Germanic tribe.
Step-by-step explanation:
To resolve a labor shortage, the Romans turned to a group of people across the Rhine and Danube Rivers who they termed 'barbarians'. Despite a history of contempt for these Germanic tribes, the Romans began incorporating them, especially the Goths, into their military as federatii - allies that provided military assistance in return for recognition and aid from Rome. In facing labor shortages, Romans were known to look outside the Empire to these barbarian groups for soldiers and workers. However, the most direct answer for the Romans calling across the Rhine and Danube for help with labor shortages would be the Visigoths, one of the Germanic tribes that interacted frequently with the Romans, eventually leading to the sack of Rome in 410 CE.