During the thousand years and more that intervene between the Arab conquest of Egypt and its conquest by Napoleon, the events in the history of Alexandria are geographic rather than political. Neglected by man, the land and the waters altered their positions, and could Alexander the Great have returned he would have failed to recognise the coast. (i) The fundamental change was in the 12th cent., when the Canopic mouth of the Nile silted up. Consequently the fresh water lake of Mariout, being no longer fed by the Nile floods, also silted and ceased to be navigable. Alexandria was cut off from the entire river system of Egypt, and could not flourish until it was restored; she has always required the double nourishment of fresh water and salt. (ii) There was also a change in the outline of the city: the dyke Heptastadion, built by the Ptolemies to connect the mainland with the island of Pharos, fell into ruin and became a backbone along which a broad spit of land accreted; and so Pharos turned from an island into a peninsula—the present Ras-el-Tin. The Arabs, though they let the city fall out of repair, admired it greatly. One of them writes as follows:— The city was all white and bright by night as well as by day. By reason of the walls and pavements of white marble the people used to wear black garments; it was the glare of the marble that made the monks wear black. So too it was painful to go out by night ... a tailor could see to thread his needle without a lamp. No one entered without a covering over his eyes. A second writer describes the green silk awnings that were spread over the Canopic Way. A third, even more enthusiastic exclaims:— I have made the Pilgrimage to Mecca sixty times, but if Allah had suffered me to stay a month at Alexandria and pray on its shores, that month would be dearer to me. The Arabs were anything but barbarians; their own great city of Cairo is a sufficient answer to that charge. But their civilisation was Oriental and of the land; it was out of touch with the Mediterranean civilisation that has evolved Alexandria. At first they made some effort to adapt it to their needs. The church of St. Theonas became part of the huge “Mosque of the 1,000 Columns;” the church of St. Athanasius also became a Mosque—the present Attarine Mosque occupies part of its site; and a third Mosque, that of the Prophet Daniel, rose on the Mausoleum of Alexander. But the Caesareum, the Mouseion, the Pharos, the Ptolemaic Palace, all became ruinous. So did the walls. And though the Arabs built new walls in 811, their course is so short that they vividly illustrate the decline of the town and of the population. (See map p. 98). They only enclosed a fragment of the ancient city.