The last of the great tower castles may be Richard the Lion Hearted’s French castle Chateau Gaillard (see Chapter 2), built after his capture and ransom in 1192–93. In spite of the terrible strain that Richard’s ransom had placed on the English treasury, the castle was built rapidly. After Richard’s death the strength of the tower, the double walls and ditches, and the complex forebuildings did not save the garrison at Chateau Gaillard. The castle fell to the French king in 1204. As castle design evolved, the great tower was eventually replaced by walled enclosures, which permitted more effective use of troops and better living conditions. The future of castle design lay with the curtain wall, that is, a wall “hung” like a curtain between towers, each of which functioned like a keep. The builders of the walls of Constantinople had seen the virtues of wall towers and curtain walls centuries earlier, and western crusaders who passed through Constantinople had the opportunity of studying these ancient fortifications.