When stone castles began to dominate the landscape of continental Europe and England in the twelfth century, they changed the nature of warfare. Large forces no longer clashed in full-scale battles. Instead, as historian N. J. G. Pounds explains,

The appearance of a hostile army was followed by retreat into the castle and reemergence when the danger had passed. There were skirmishes and ambushes, but battles were rare. The forces engaged were small, and warfare consisted largely in destroying whatever resources might be useful to the other side; in protecting oneself in one's own castle, and in attacking the enemy in his.

Once the object of making war had been to defeat an opposing lord's army—which inevitably meant losing many of one's own men in the process. Now the object was to weaken an adversary's control and strengthen one's own by capturing...