From the back cover:
Welcome to the age of chivalry, fealty and piety. GURPS Middle Ages 1 takes you to the rich, dark world of medieval England, where heroic knights fight for King and God, nobles trade favors and treachery, and peasants work the land.
Three major periods are covered: the Saxon Kingdoms, Norman England and the High Middle Ages. Each has a distinctive flavor and campaign style - combined with the cinematic "Hollywood Middle Ages," they provide a complete guide to medieval roleplaying.
From simple jousts to the deadly Crusades, combat in the Middle Ages is covered in detail, with complete descriptions of melee weapons, siege weapons, armor and castle defenses. Also included are chapters on magic, religion and creatures of fact and fantasy, and maps of castles, an abbey, and medieval England and France.