A fyrd was a type of early Anglo-Saxon army which was mobilized by freemen to defend their shire in times of war. The Germanic rulers in early Middle Ages-era Britannia relied upon a regional levy to fight off invaders, and landed nobles would be fined and forced to forfeit their lands if they refused to fight, while commoners would pay a 30-shilling fine for refusing to serve. Originally, the fyrd consisted entirely of thegns and peasants serving as infantry, but, during the reign of Alfred the Great, cavalry became a part of the fyrd. Alfred replaced the fyrd with a system of feudalism, setting up 33 fortified towns (burhs) in Wessex, paying for their upkeep with tax money, and obligating landed nobles to contribute men and arms to defend the burhs.