The defeat of the Sotiates (56 B.C.) was the first of two major battles in unknown locations in which Publius Crassus, the son of the Triumvir and one of Caesar's most able lieutenants, defeated the Aquitani tribes of south-west Gaul.
Caesar's invasion of Aquitania was one of his most blatantly aggressive moves. In the summer of 56 B.C. Caesar was campaigning against the maritime tribes of north-west Gaul, led by the Veneti, but the Aquitani had not taken part in that rebellion. Caesar would have been justified in watching the line of the Garonne, which marked the border of Aquitani territory, but instead he chose to send Publius Crassus, with twelve infantry cohorts and a large cavalry detachment, into Aquitania 'lest auxiliaries should be sent into Gaul by these states'.
Crassus was aware that he faced a difficult task, and so when he reached Aquitania (presumably from the north, where Caesar's army had spent the previous winter), he summoned extra auxiliary troops and cavalry from the nearby Roman Province in southern Gaul. This reinforced army then advanced into the territory of the Sotiates tribe.
The Sotiates planned to draw Crassus into an ambush. Their infantry was placed in a position where they could attack the Romans as they passed through a valley, and their strong cavalry force was used to lure the Romans in.
Crassus fell into the trap. The Sotiates cavalry attacked the Roman column while it was on the march. The cavalry was duly defeated, and the Romans began a pursuit which brought them into the valley where the Sotiates infantry was waiting. As the Romans passed through the valley in some disorder, they were duly ambushed. At this point the Sotiates plan began to go wrong. Order was quickly restored in the Roman force, and after a long fight the Sotiates broke and fled, suffering heavy casualties in the process.
After this victory Crassus advanced deeper into Sotiates territory and began to besiege their principle towns. After a number of sorties failed to drive off the Roman siege forces, the Sotiates surrendered, freeing Crassus to move against the Vocates and Tarusates.