What Were the Crusades? Two Centuries of Holy War Explained

Jerusalem had been under Muslim rule since 638, and Christian pilgrims had mostly been allowed to visit it. What changed was the arrival of the Seljuk Turks, who took the city in 1071, defeated the Byzantine Empire at Manzikert the same year, and overran Anatolia, so that the Byzantine emperor Alexius appealed to the pope for mercenaries to help him win it back. Urban turned a request for troops into something new: an armed pilgrimage in which fighting was itself the penance. Europe was ready for it. The eleventh century had produced a warrior aristocracy with too many younger sons, a reformed papacy asserting its leadership over Christendom, a growing population and a religious enthusiasm that the Church had been trying to channel away from private war. The crusade offered all of them land, glory and heaven at once.

The first to set off were not knights but a mob of peasants led by a preacher called Peter the Hermit, who murdered Jewish communities in the Rhineland on the way and were wiped out by the Turks in Anatolia. The knights followed in 1096 under a group of French and Norman lords with no overall commander, took Nicaea and Antioch after sieges of appalling hardship, and on 15 July 1099 stormed Jerusalem and killed most of its Muslim and Jewish inhabitants. They set up four states along the coast of Syria and Palestine, the Kingdom of Jerusalem chief among them, and held them for most of a century with the help of the military orders, the Templars and Hospitallers, monks who fought. The main expeditions that followed:

• •Second Crusade, 1147 to 1149: launched after the loss of Edessa, led by the kings of France and Germany, and a failure that besieged Damascus for four days and went home
• •Third Crusade, 1189 to 1192: after Saladin retook Jerusalem in 1187, Richard the Lionheart, Philip of France and Frederick Barbarossa set out; Frederick drowned, Philip left, Richard won battles but not the city, and settled for pilgrim access
• •Fourth Crusade, 1202 to 1204: diverted by debts to Venice, it never reached the Holy Land and instead sacked Constantinople, the greatest Christian city in the world, and broke the Byzantine Empire
• •Fifth to Eighth, 1217 to 1270: attacks on Egypt and Tunis that failed, though Frederick II regained Jerusalem by treaty for fifteen years in 1229 without fighting
• •1291: the fall of Acre, the last crusader city on the mainland, to the Mamluks of Egypt

The idea, once invented, was applied wherever the papacy had enemies. Crusades were preached against the Muslims of Spain, whose reconquest took until 1492; against the pagan Balts and Slavs of the north, where the Teutonic Knights carved out a state that became Prussia; against the Cathar heretics of southern France, in a war of extermination from 1209; and against the pope's political opponents in Italy. The Children's Crusade of 1212, in which thousands of young people set out for the Holy Land and were sold into slavery or turned back, is partly legend. The crusade was less a series of events than an institution, with its own law, taxation and vows, that lasted into the sixteenth century.

To the Muslim world the crusaders were Franks, a barbarian people from the edge of the map, and their first successes were possible because the Islamic Middle East was divided between rival dynasties too busy with each other to unite against them. The man who ended that was Saladin, a Kurdish officer who took control of Egypt and Syria, destroyed the crusader army at Hattin in 1187 and took Jerusalem with none of the slaughter of 1099. Islamic writers of the time paid the crusades far less attention than European ones did; the invasions were one episode among many, and the Mongol destruction of Baghdad in 1258 was a far greater catastrophe. It was in the nineteenth century, when European empires returned to the region, that the crusades were rediscovered in the Arab world as the first chapter of a long story, and Saladin became a modern hero.

The crusades failed at their stated purpose: Jerusalem was Christian for eighty-eight years out of two hundred and has been under Muslim rule for most of the time since. Their effects were elsewhere. They opened the trade of the eastern Mediterranean to Venice and Genoa, which grew rich on it; they brought Europe sugar, paper, new crops and the Arabic learning through which Aristotle returned; they gave the papacy a means of raising money and armies that it used for centuries; and they left in Europe a habit of thinking about war against unbelievers as holy that shaped the conquest of the Americas. They also left the Jews of Europe with the memory of the massacres of 1096, the first of many, and the Christians of the east, sacked in 1204, with a grievance against the west that has not entirely faded. Historians disagree about whether the crusaders were mostly pious or mostly greedy, and the answer from the sources is that most of them were both, and that the enterprise was as expensive as it was devout; a crusading knight typically sold or mortgaged land worth several years' income to go, and most never came back.

The Crusades were the wars from 1095 to 1291 in which the papacy summoned the knights of Europe to take and hold Jerusalem as an armed pilgrimage that earned forgiveness of sins. The First Crusade took the city in 1099 and founded states that lasted until the fall of Acre; the later expeditions mostly failed, and one destroyed Constantinople instead. They enriched the Italian ports, brought eastern learning west, and left a legacy of holy war and of grievance on every side.