The core of feudal armies was formed by mounted men-at-arms—not all of them knights. The ability to fight on horseback, as opposed to merely arriving by horse on the battlefield or engaging with the enemy at bow-shot distance, had been hugely enhanced in the 8th century with the arrival in Europe of the stirrup, which gave a mounted warrior a much more stable platform from which to employ swords or spears. The characteristic dress of such 11th- and 12th-century fighters is summed up in the 1181 Assize of Arms of Henry II of England, which declared "let every holder of a knight’s fee have a hauberk (coat of mail), a helmet, a shield and a lance." Such armies were expensive to maintain and inflexible, and as the obligatory period of service was so short, campaigns could not be long. This, and the need to avoid casualties among the hard-to-replace heavy cavalry, meant that the raid or chevauchée came to be the standard form of warfare. Pitched battles were relatively rare, although those large-scale battles that did occur, such as the defeat of the English king Harold II by the Norman Duke William at Hastings in 1066, were all the more decisive for it. William’s army is depicted on the Bayeux Tapestry clothed in mail and sporting conical helms. A large portion of the Norman army was, in fact, composed of archers, with shortbows or mechanical crossbows. At Hastings, massed volleys of arrows, combined with hit-and-run cavalry attacks, overcame the English shield wall manned by Harold’s huscarls, warriors of undoubted effectiveness wielding two-headed axes, but who lacked the mobility to counter the Norman tactics.