Nor did the caliphs extort taxes without giving something in return. The development of irrigation works was always a main consideration with the early Mohammedan rules, from Spain to India, and in Egypt, where irrigation is the country's very life, it was specially cared for, with a corresponding increase in the yield. Moreover, the governors usually held to the agreement that the Christians should have liberty of conscience, and protected them from the Moslem soldiery. As time went on, this toleration abated, partly because the Moslems had gradually become the predominant population. At the beginning the caliphs had taken anxious precautions against the colonising of Egypt; they held it by an army, but they were insistent that the army should not take root, but be always free to join the caliph's standard. But it was inevitable that the Arabs should settle in so fertile and pleasant a land. Each governor brought a small army as his escort, and these Arab troops naturally intermarried with Egyptian women, who were constitutionally inclined to such alliances. A few Arab tribes also settled in Egypt. This gradual and undesigned Arabising of the country would lead to oppression of the Christians, to the "squeezing" of wealthy natives, and occasionally to the institution of humiliating distinctions of dress and other vexations, and even to the spoiling of Coptic churches. Then sometimes the Copts, as the Egyptian Christians are called, would rebel. Their last and greatest rebellion, which occurred in the Delta in 830-832, was ruthlessly trampled out by Turkish troops under Mamun, the only Abbasid caliph who made a visit to Egypt. Many Copts now apostatised, and from this time dates the predominance of the Moslem population and the settling of Arabs in the villages and on the land, instead of as heretofore only in the two or three large towns. The coming of the Turkish troops with the caliph Mamun was an ominous event for the country. Up to 846 all the successive governors had been Arabs, and many of them were related to the caliphs themselves. With some unfortunate exceptions, they seem to have been men of simple habits--the Arabs were never luxurious--and usually of strict Mohammedan principles. They made money, honestly if possible, during their brief tenure; but they did not harass the people much by their personal interference, and left the local officials to manage matters in their own way, as had always been the custom. They lived at the new capital, Fustat, which grew up on the site of the conqueror's camp, and very near the modern Cairo; for Alexandria, the symbol of Roman domination, was dismantled in 645 after the Emperor Manuel's attempt at reconquest. If they did not do much active good, they did little harm, and Egypt pursued her immemorial ways.