With Ridley Scott's Crusades epic opening in cinemas next week, Nick Morrison looks at the two-century long battle between Christians and Muslims whose impact is still felt today.

"WE are freedom's home and defender. This crusade, this war on terrorism, is going to take a while, but we will rid the world of the evil-doers." President Bush's words a few days after the 9/11 attacks prompted barely a ripple in the United States, but caused fury among Muslims and consternation in Europe. Not for the promise to hunt down the "evil-doers", but for invoking the memory of a religious struggle whose scars have still to heal.

Spread over almost 200 years, the Crusades pitted Christian against Muslim in a battle for the Holy Land. A series of brutal conflicts, advantage swayed first one way, then the other. Whole populations were massacred and cities destroyed - and all in the name of faith.

It is into this context that Sir Ridley Scott's film Kingdom of Heaven opens in cinemas next week. The South Shields-born director takes the collision between Christianity and Islam as his subject in one of the most eagerly-awaited movies of the year.

His film has been denounced as "anti-Islamic", a replay of historic stereotypes of the "barbaric" Saracens and offensive to Muslims. Alternatively, Sir Ridley was accused of presenting the Arabs in too favourable a light and pandering to Islamic fundamentalists. And this was before filming even started.

The movie tells of Balian, a young blacksmith searching for answers after the death of his wife and son. Claimed as his illegitimate son by the knight Godfrey of Ibelin, Balian accompanies him to the Holy Land, to help preserve the fragile peace between King Baldwin of Jerusalem and the Saracen leader Saladin.

Once there, Balian falls under the spell of the king's sister Sibylla and becomes caught up in the intrigues of Baldwin's court, as extremists threaten to destroy the truce - the "kingdom of heaven" - and Jerusalem again comes into peril.

Although there have been liberties with history, the film is based on historical fact, set between the Second and Third Crusades. Balian of Ibelin, the character played by Orlando Bloom, led the defence of Jerusalem against Saladin in 1187, although he was born a knight, not a blacksmith. King Baldwin IV, stricken by leprosy, did preside over a period of peace.

It was a pope who prompted one of the most bloody episodes of medieval history. In November, 1095, Urban II spoke to an assembly of knights, nobles and clerics at the Council of Clermont, in France. Jerusalem, he said, had fallen to an "accursed race", who had desecrated Christian sites. It was the duty of all followers of Christ to rescue the Eastern Church and liberate the Holy Land. For those who believed killing was wrong, Urban had an answer. "If you must have blood, bathe in the blood of infidels," he said.

For hundreds of years, Christians had made the arduous pilgrimage to the Holy Land to visit the scenes of Christ's life. But in the middle of the 10th century, the Seljuk Turks expanded westwards from their homeland in Central Asia, and by 1071 Jerusalem had fallen.

Urban saw the Crusades not only as a means of freeing the Holy Land from Muslim control, but also as a way of extending the influence of the Roman Church into the Byzantine Empire, which had split from Rome in the collapse of the Roman Empire.

The promise of glory and redemption, not to mention the riches of plunder, proved irresistible to European knights more used to fighting in exhausting squabbles for little reward.

But the first Crusaders were not knights, they were a mob of peasants. Peter the Hermit recruited 15,000 followers from France and Germany and set off for the Holy Land in the spring of 1096. As they crossed Europe, they left a trail of chaos, burning houses and stealing. They quarrelled amongst themselves, killing Jews and Christians alike, and were eventually massacred by the Turks.

Six months later the pope's army of knights departed. This First Crusade marched to Constantinople and then into Asia Minor, sweeping the Turks before them. Jerusalem was stormed in July 1099, and became one of four Crusader states, the others at Edessa, Antioch and Tripoli.

Godfrey of Bouillon became the first ruler of Jerusalem, succeeded by his brother Baldwin, although the real rulers of the Crusader states were the military orders of knighthood, the Knights Templar and the Knights Hospitaler, the most effective fighting forces in the Holy Land.

By the early 12th century, the Turks had begun to fight back, and in 1144 took Edessa. This prompted the Second Crusade, this time led by Louis VII of France and Conrad III of Germany. But relations with Byzantium had deteriorated, the armies were almost wiped out in Asia Minor and they failed to take Damascus.

In 1169, the Turkish armies came under the command of Salah al-Din Yusuf Ibn Ayyub, known as Saladin. Born in Tikrit, in modern-day Iraq, he was the greatest Muslim leader of the Crusades, chivalrous and humane, as well as an astute general.

In 1187 Saladin defeated the Crusaders' forces at Hattin and went on to take Jerusalem, prompting a Third Crusade, led by the Holy Roman Emperor Frederick Barbarossa, although he drowned before he reached the Holy Land. His troops carried on, however, and were joined by Philip Augustus of France and Richard the Lionheart of England. Although the Crusaders captured Acre, they failed to take Jerusalem, settling for signing a treaty to allow Christians to visit the city.

It was another pope, Innocent III, who urged the Fourth Crusade in 1198, although this went spectacularly awry. The Crusaders sacked the Catholic port of Zara on the Adriatic, and then proceeded to a three-day sacking of Constantinople in 1204, destroying valuable treasures including libraries and art collections. They were excommunicated for their troubles.

Perhaps the most tragic Crusade was the Children's Crusade of 1212, which started simultaneously in the Rhineland and the Loire Valley. Around 20,000 children left Germany, led by a ten-year-old boy, Nicholas, but when they reached Italy many of the girls were taken into brothels and those who continued to the east were sold as slaves. The 30,000 who left France, led by a 12-year-old called Stephen, were sold as slaves at Alexandria or drowned in the crossing from Marseilles.

The Fifth Crusade in 1218 attempted to recapture Egypt but failed miserably. Emperor Frederick II led the Sixth Crusade in 1228 but no fighting was involved. Instead, he achieved more by negotiation, restoring Jerusalem to the Latin world and signing a ten-year truce.

But this was to be the last high point of the Crusades. The Seventh Crusade in 1248 collapsed when its leader, Louis IX of France, was captured and had to be ransomed. Two later Crusades were just as ignominious. The Turks gradually pushed the Crusaders out of their strongholds, until their final city, Acre, fell in 1291.

The Crusades did see an exchange of cultures between Christian and Muslim, and the rediscovery of knowledge which had been preserved by Islamic scholars is credited with sowing the seeds for the Renaissance.

In the Muslim world, the Crusades had initially attracted little attention. Jerusalem was on the outskirts of the Muslim world and it was only later that it was seen as a prize to be recaptured. But for the Christians of the west, the Crusades represented the first time they had been on the offensive against Islam, heralding a new age of optimism and religious revival, despite the ultimate failure. The cost was that it was achieved through savage butchery, it contributed to the collapse of the Byzantine Empire, caused lasting wounds between Christian and Muslim and began a history of western colonialism in the Holy Land.

* Kingdom of Heaven opens in cinemas on Friday

* Interviews and reviews: see 7DAYS on Thursday