From the seventh century onwards, at the time that Islam was growing among Arab peoples, the peaks of human culture were at Constantinople, Baghdad and Cairo. Without the work of Arab scholars at this time, much of Greek and Roman literature would be lost. Western cities like Paris, and even Rome, were considered by the the Arab world to be occupied by barbarians.

In 638 Caliph Omar captured the city of Jerusalem for a growing Arab empire. When visiting the Church of the Holy Sepulchre, the most revered site of Christian worship, the time for Muslim prayer approached. The Caliph was urged to stay and pray, but he left and used the porch, saying that he did not want to set a precedent which would encourage his zealous followers to claim the church for their own.

This incident illustrates the fact that for centuries after Jerusalem fell into Islamic hands, there was religious tolerance in the city. Under Arab rule, Christians and Jews retained their places of worship and could use them without hindrance. In fact they paid less tax than under the previous Christian administration. A ninth century letter from the Patriarch of Jerusalem says of the Muslim authorities, "they are just and do us no wrong, nor show us any violence."

There is no evidence for large numbers of Arabs entering Syria and Palestine in these centuries, so the people who are called 'Arab' today are largely the descendents of a formerly Christian and Roman population who adopted Arabic and Islam - which at the time was considered to be merely an advanced and more rational form of Christianity.

However, at the end of the eleventh century a movement was unleashed that destabilised the status quo of the Middle-East and led to bitter religious conflict - 'the crusades'.

At Clermont On 27, November, 1095, Pope Urban II made an appeal to his French audience to cease fighting one another and turn to the East against non-Christian enemies. Urban might well have been wanting to raise a force in response to an appeal for help by the Orthodox Christian Emperor at Constantinople - but what he unleashed was a massive movement which aimed at the capture of Jerusalem.

The Pope had tapped the energy not only of genuine religious fervour, but also that created by the circumstances of life in Northern Europe.

For the peasantry, the idea of a crusade came as an opportunity escape from servitude and a land suffering from drought, plague and famine. Following itinerant preachers, thousands of peasant families put all their belongings onto a cart and headed east. Women joined the movement seeking freedom from the strict control of feudal society over their lives.

For the nobility life had become more restrictive during the eleventh century. The customary way for a young prince to make his way in the world was through war, against neighbours, family and peasantry, until a suitable realm was won or he had died in the attempt. But this route to the ownership of land was being squeezed, from above by the control of the great kings and Dukes, and from popular mobilisations of villagers in the 'Peace of God' and 'Truce of God' movements.

As a result, many knights rallied to the idea of the crusade. Here was a chance to earn fame and fortune in the east and at the same time earn the blessings of a Church which had been hostile to their local plundering.

By 1096 thousands of people, from all layers of society, were underway and heading for Jerusalem. As they travelled they proved to be an incredibly destructive force, both to Christians and non-Christians. One German contingent only got as far as Worms and Mainz, dispersing after they had massacred the local Jewish population.

In 1099, after immense hardship that had seen most of the poorer crusaders die from starvation or be taken away into captivity as slaves, the First Crusade reached Jerusalem. When the city was captured, it was with an orgy of destruction. The entire Muslim and Jewish population of the city was wiped out, blood flowed through the streets to such an extent that crusaders were soaked to their knees in it. A contingent of Muslims had been offered refuge at the mosque of al-Aqsa but early on in the morning, the day after the capture of the city, soldiers forced their way into the mosque and slaughtered everyone. Many of those in the building preferred to leap do their deaths from the roof than be put to the sword.

That the violence was so great was not only due to religious sectarianism but the fact that the surviving poor crusaders had no intention of returning to Europe and had only agreed to storm the city on condition that they could take over homes there. The massacre at Jerusalem shocked the civilised world, and the nearby muslim populations were never to forget it.

For nearly a century a small Christian kingdom based on Jerusalem existed in the Middle-East. That they were able to survive was largely because they formed a useful buffer state between two great rival Arab empires based on Cairo and Baghdad. The crusaders themselves began to adapt to local conditions. They inter-married with the local population, learned the language, began to dress, eat and behave like Arabs. It might have been possible for the crusader state to integrate with the Arab world but for the constant influx of fanatical Christian warriors. The military - religious orders of Hospitalars and Templars saw integration as treachery and destabilised the efforts of the kings of Jerusalem to form treaties with local Arab rulers.

As a consequence, the great general Saladin was able to unite the Arab world against the Crusader states. In 1187 Jerusalem fell to Saladin's army. By contrast with the crusaders, Saladin was relatively generous with his defeated enemy. Not a building was looted and not a person injured. Saladin posted patrols to keep the streets peaceful.

Saladin offered the rulers of Jerusalem a chance to redeem the 20,000 Christian captives before they were led away to slavery. He set a price which he knew the authorities could well afford. But Muslims were shocked when the Patriarch of Jerusalem paid just ten dinars for his own ransom and left the city, unmolested, with a large train of carts laden with gold, silver and carpets. The plight of the remaining Christians was so pitiful that Saladin unconditionally freed all the elderly men and women and several thousand others.

The Papacy and the European nobility did not give up on the idea of recapturing Jerusalem, but over the years the idea of a crusade became discredited as crusading armies attacked fellow Christians. In 1204 a crusade directed against Christians of the East sacked Constantinople. It was followed soon after by a crusade against the heretics of southern France and later against the German Emperor. The spiritual system of indulgences and heavenly reward was debased. The concept of Holy War became a farce.