Gauls
In 58 BC Julius Caesar launched the Gallic Wars and had conquered the whole of Gaul by 51 BC. He noted that the Gauls (Celtae) were one of the three primary peoples in the area, along with the Aquitanians and the Belgae. Caesar's motivation for the invasion seems to have been his need for gold to pay off his debts and for a successful military expedition to boost his political career. The people of Gaul could provide him with both. So much gold was looted from Gaul that after the war the price of gold fell by as much as 20%. While they were militarily just as brave as the Romans, the internal division between the Gallic tribes guaranteed an easy victory for Caesar, and Vercingetorix's attempt to unite the Gauls against Roman invasion came too late. After the annexation of Gaul a mixed Gallo-Roman culture began to emerge.
Publius Licinius Crassus (son of triumvir)
In the first year of the Gallic Wars, Caesar and his Celtic Aeduan allies fought a defensive campaign against the Celtic Helvetii, and waged an offensive against the Germanic Suebi and their allies, led by Ariovistus. During the decisive battle against the Suebi that brought the first year of fighting to its conclusion, Publius Crassus was given command of the cavalry. In 58 BC, Caesar's cavalry auxiliaries numbered 4,000, comprising regiments from the Aedui and from the Gallic nations of Gallia Transalpina, already a Roman province. In Caesar's army, the primary strategic applications of cavalry were reconnaissance and intelligence gathering, conducted by detachments of "exploratores" (“scouts”) and "speculatores" (“spies”); communications; patrols, including advance parties and guard units on the flanks of the army on the march; skirmishing, and securing the territory after fighting by preventing the flight of surviving enemy. The cavalry charge was infrequent. In the opening stage of the war against the Helvetii, Caesar had retained a Gallic command structure; a lack of strategic coordination, exacerbated by conflicting loyalties, led to poor performance, which Caesar sought to correct with a more centralized command. Publius Crassus is the first Roman named as a cavalry commander in the war, and was perhaps given the task of restructuring.