Warfare had become endemic in eleventh- and twelfth-century Europe. Castle building used up the resources of the land as every landholder from the king and great nobles to the small landholders fortified their dwellings. Constant skirmishing, brigandage, and open warfare at home and abroad meant that people poured vast resources into training and equipping warriors and building castles and siege machines. The motte and bailey castle with its great tower, as the keep or donjon is called in medieval documents, was admirably suited as a defense against local skirmishes. The castle was also a symbolic expression of its owner’s power and pride (Figure 11). During the twelfth and thirteenth centuries, as kings and nobles tried to form larger estates and nations, they built massive stone castles. Cities and towns sought to define and defend their borders by building walls and fortified gates. Even churches and monasteries had defensive walls. At the city of Avila, Spain, the cathedral apse formed one of the most powerful towers in the encircling walls, and in northwest Spain, the cathedral of Santiago de Compostela had to withstand a siege. Even monasteries like the Abbey of St. Denis just north of Paris in France had crenellated walls. In the nineteenth century the French architect Violletle- Duc restored the walls and towers of Carcassonne. Today the old city gives us a romanticized idea of medieval fortifications (Figures 11, 12, and 13). The emergence of Islam as an international religion and the success of Muslim armies also energized Christian forces and drew them into wars where tactics—and castles—became increasingly sophisticated. Jerusalem as the holy city of three faiths—Jewish, Christian, and Muslim—remained the focus of western European thought and pilgrimage even though the city and the holiest sites in Christendom lay in Muslim hands. Muslims also controlled northern Africa and the Iberian Peninsula. In the ninth century St. James miraculously appeared in northern Spain to turn the tide of battle, leading Christian forces to victory and so beginning the Christian reconquest of the Iberian Peninsula. At the end of the eleventh century (1095) Pope Urban II traveled through France preaching a crusade to liberate Jerusalem. French, Flemish, German, and English nobles joined in the enterprise. The First Cru sade left in 1096, Christians captured Antioch in 1098, and by July 1099 Jerusalem again lay in Christian hands (Documents 29–32). The crusaders established Christian kingdoms in Palestine and Syria, ruled by the warriors Bohemund in Antioch and Godfrey of Bouillon and then Baldwin in Jerusalem. But Muslims captured Christian Edessa in 1144, and in 1147 the Christians mounted the Second Crusade. When the Muslim leader Saladin (r. 1174–93) recaptured Jerusalem in 1187, the kings of western Europe—Frederick Barbarossa of Germany (r. 1152–90), Philip Augustus of France (r. 1180–1223), and Richard the Lion Hearted of England (r. 1189–99)—rallied the Christian forces yet again. The Third Crusade ended in a truce. Mythmakers glorified the leaders: Saladin and Richard became models for the perfect knight. Frederick, who drowned before even reaching the Holy Land, supposedly was only sleeping until called again to save the German people. Only Philip Augustus was not glorified by the troubadours, and only he profited from the Crusades. As an astute politician, Philip Augustus emerged as the leader of the everlarger and more powerful nation of France. The Crusades led to rapid developments in castle design as the combatants studied each other’s buildings and weapons. The most sophisticated and skilled military engineers had been the Byzantines. As early as the “Golden Age” of Theodosius and Justinian in the fifth and sixth centuries, the Byzantines knew the advantages of double walls staggered in height, independent projecting wall towers, round rather than squaredoff corners, masonry built up in alternating bands of stone and brick, and heavily fortified gateways. Christians and Muslims alike had the mighty walls of Constantinople before them as models (see “Overview: Castles in Context”). Muslim military engineers paid special attention to gateways and invented the most complex turns and traps, murder holes and arrow slots, portcullises and drawbridges. The crusaders, as invaders without a local support system, became painfully aware of the problems of supplying their forces, and they added huge water reservoirs and storage facilities within their castle walls. When these warriors returned to their homelands, they took with them the experience gained in the Holy Land. In the twelfth century, sophisticated defense systems appeared throughout Europe. Intermittent warfare between Christians and Muslims in the Iberian Peninsula, Syria, and Palestine also led to cultural as well as military exchanges. Crusaders returning to their homes in western Europe brought back new ideas of luxurious living (spices, perfume, carpets, and pieces of richly inlaid metal), new plants (rice, lemons, melons, and apricots), and new technology (water wheels, windmills, and chimneys). The knightly order of the Templars established a rudimentary international banking operation leading to new opportunities for merchants and rulers. Finally, the experience of travel led to further exploration, and gradually European society changed.