The Cambridge History of Warfare

Although men had fought on foot throughout the Middle Ages, in the course of the thirteenth century infantry began to assume an increasingly significant role in Western warfare. The crossbow, albeit condemned by the Church, appeared in action with greater frequency, posing a considerable threat to the mounted warrior and his horse; the longbow, which could discharge arrows at the rate of about ten a minute (in contrast to the much slower rate of two bolts from the crossbow), could penetrate chain-mail armour with ease. The gradual introduction of plate armour from around 1250, to reinforce chain mail, reflects the recognized need to respond to the development of the bow, which would continue to influence the way war was fought for a century and a half.