During the summer of 52 BC, following the fights that opposed him to the Roman legions during their withdrawal towards the Roman province of southern Gaul, Vercingetorix decided to install his troops (80,000 men, according to Caesar) in the oppidum of Alesia in Burgundy. Caesar, at the head of ten to twelve Roman legions (40 to 45,000 men) supported by several thousand auxiliaries and German horsemen, then surrounded the Gauls with a double row of fortified lines preceded by a set of very elaborate traps and laid siege to the oppidum. After a first defeat, the horsemen of Vercingetorix left to seek reinforcements throughout Gaul. Meanwhile, the Roman fortifications grew and the Gallic troops starved. When the relief army of 240,000 infantry and 8,000 cavalry (according to Caesar) finally arrived, they were routed. Withdrawn into the oppidum, Vercingetorix finally chose to surrender to spare his men after a siege that had lasted an estimated one and a half or two months.