The most spectacular and prestigious siege engine was the belfry or moveable tower (Documents 28 and 39). Only kings and great lords could afford such an expensive piece of woodwork. These towers must have been masterpieces of carpentry, for they had to be as tall as the castleís towers and walls. After filling the ditches and moats the men hauled the finished tower across the causeway and into place beside the wall. In theory, the knights climbed to the upper platform, a drawbridge was dropped from the tower to the castle wall, and the attackers rushed out to engage in hand-to-hand combat. This was the kind of battle for which the knights had trained since childhood. But problems are obvious. Although wet hides made the towers almost fireproof, they could be set on fire, turning them into ovens that roasted the men inside. They could also be toppled over, crushing their users.