Cimbri

On October 6, 105 BC, at the Battle of Arausio, the Cimbri inflicted the heaviest defeat on the Roman army of Gnaeus Mallius Maximus. An excerpt from the article:

"The Cimbri were a tribe who lived in northern Jutland during the Roman era. Their ethnicity is enigmatic; scholars generally believe that the Cimbri were Germans, though others maintain that they were Celts. The late 2nd-century BCE migration of the Cimbri led them to the Balkans, over the Alps, throughout Gaul, along the borders of Spain, and finally into Italy. They were joined by other Germanic and Celtic tribes; most notably the Teutones who were their neighbors in Jutland and shared much of their history. The Cimbri coalition reached the frontiers of the Roman Republic, where they fought and defeated multiple Roman armies. Their victory at Arausio (Orange) in 105 BCE, was one of the greatest disasters in the history of Roman warfare. The Cimbri entered Italy in 102 BCE when under the leadership of Boiorix they crossed the Alps and settled north of the Po. The following year, they were decisively defeated at Vercellae by the Roman commanders Marius and Catulus. Survivors of the battle were enslaved, but fragments of their tribe continued to live for centuries in eastern Gaul and in their Jutland homeland."