Charles' army had 10,000-40,000 troops; he divided it in half, giving command of one half to his uncle, Bernard, son of Charles Martel, and led it through the Alpine passes; he through that of the Dora Susa near Mont Cenis, and Bernard through the Great St Bernard Pass. At the foot of the mountains, Charles' army met the fortifications of Desiderius, but scouting forces found an alternate route. A cavalcade was sent to attack the defenders from the flank and, with Bernard's forces approaching from the east, the Lombards fled to fortified Pavia. The Frankish troops then marched on to begin the siege of Pavia by September.