"The development of feudalism," writes historian Joan Evans, "is reflected in the development of the castle." In the ninth and tenth centuries, when warring factions in Europe were numerous and relatively small, castles were small and simple affairs, meant mainly to provide a place for a lord and his knights to hole up temporarily when they were under attack.

But as the size of the great lords' feudal "families" grew, so did their castles. They were transformed from temporary fortresses into full-time living quarters. In fact, a castle is, by the usual definition, designed for more than just defense. It is also meant to be a home. It is, in other words, a fortified residence.

The Earliest Castles

Castles of various sorts were common throughout Europe during the Middle Ages—in Belgium, Switzerland, the Netherlands, Germany, and Italy. They...