The last attempt at a passage from the Red Sea to the Nile was made by Amru ibn el Aas, the general of the Caliph Omar, who conquered Egypt in the seventh century. A great famine reigning in Mecca, Amru was ordered to take measures for forwarding thenceforth grain from Egypt by the quickest route. “He dug a canal of communication from the Nile to the Red Sea, a distance of 80 miles, by which provisions might be conveyed to the Arabian shores. This canal had been commenced by Trajan, the Roman emperor,”[141] who, the Pelusiac arm of the Nile being no longer navigable, joined his canal to the river at Cairo, instead of Bubastis or Zigazig. This occurred in the year of the great mortality A.D. 639, and in 767 the Caliph Abou Giaffar el Mansour, to prevent food being sent to the insurgents of Medina, caused the canal to be destroyed by filling up the junction of Neco’s canal and the Bitter Lakes. The winds and the sands completed the work, and produced the ridge of Serapeum, which is believed by some to cover the site of the ancient city of Heroopolis. The engineers of Ptolemy II. advised him not to cut a canal across the isthmus, because the land, being lower than the level of the Red Sea, would be laid under water; but that prince turned the difficulty by causing flood-gates to be erected at proper points, in order to keep back the waters of the sea at high tides, and those of the canal at low ebb, so that navigation became possible both ways. Now, this opening, in as perfect state of preservation at certain places, according to M. de Lesseps, as it was in the eighth century, really forms part, to the extent of four kilometres, near Shaloof, of the present canal, which opens into the Red Sea by means of sluices having a fall of three metres (9 feet), being the altitude of the mouth above the average level of the sea. This seems to prove that eleven centuries ago the sea was about as much higher as it is now, so that the isthmus has, indeed, experienced an upheaval. At the time that the Hebrews quitted Egypt the rock of Shaloof, the last offshoot of the Geneffay Hills, must have been entirely under water. When, by the gradual rising of the land, the top of this rock emerged from the water, it became covered with an accumulation of earthy or sandy matter, brought by wind and tide, until a barrier was formed which could only be swept over at high water. The lakes were consequently precluded from experiencing any ebb or flow. The slow upheaval of the soil continuing, the _terra firma_ of Shaloof assumed a permanent shape, and the requirements of navigation led to the idea of cutting a canal. Herodotus speaks of it as having been open in his time: this fixes its date at 450 years B.C. It was repaired under the Ptolemies, improved during the Roman domination by a supply of water from Cairo, dredged by the Caliph Omar in the seventh century, and abandoned to decay in the eighth.