 Harclay had deployed his men on foot to hold the bridge from the northern side . Additional forces were placed at a nearby ford , though contemporary sources do not specify the exact location of this ford . The royal pikemen were deployed in a schiltron formation , a tactic learned from the Scots in the Scottish wars . The formation proved effective against the oncoming cavalry . The rebels divided into two columns ; one led by Hereford and Roger de Clifford , attacking the bridge on foot , the other under Lancaster , trying to cross the ford by horse . According to a graphic description in the chronicle the Brut , Hereford was killed as he crossed the bridge by a pikeman hiding underneath , who thrust his spear up through the Earl 's anus . Clifford was also severely injured , and that column of the army fell into disarray . Lancaster 's party fared little better ; under heavy archery fire his cavalry was cut off before it even reached the ford , and was forced to retreat . This event shows an early – if not entirely novel – effective use of the longbow against cavalry , a tactic which was to become central to future English military success . 
