When Amr had conquered Egypt, according to another account, the caliph Omar ordered him to ship rich supplies of grain to Mecca and Medina, because during the pilgrimages these cities and often the whole of Hedjaz suffered severely from famine. As it was extremely difficult to send large quantities of provisions across the desert on the backs of camels, it is supposed that to facilitate this transportation Omar ordered the construction of the canal from a point near Cairo to the head of the Red Sea. On account of his forethought in thus providing for the pilgrims to the Hedjaz, Omar received the title of "Prince of the Faithful" (Emir el-Momeneen), which thenceforth was adopted by his successors in the caliphate. One hundred and thirty-four years after this time, El-Mansur, the second caliph of the Abbasid dynasty, is said to have closed the canal to prevent supplies from being shipped to one of the descendants of Ali who had revolted at Medina. Since that time it is probable that it has never been reopened, although there is a report that the Sultan Hakim rendered it available for the passage of boats in the year A.D. 1000, after which it was neglected and became choked with sand. While not thereafter used for navigation, there were parts which during the time of the annual inundation of the Nile were filled with water, until Mehemet Ali prevented this. The parts filled during the inundation extended as far as Sheykh Hanaydik, near Toussun and the Bitter Lakes. The old canal which left the Nile at Cairo had long ceased to flow beyond the outskirts of the city, and the still more ancient canal from the neighbourhood of Bubastis, now known as the Wady Canal, extended only a few miles in the direction of the isthmus as far as Kassassin. During the construction of the Suez Canal the need of supplying the labourers with fresh water was imperative. The company, therefore, determined in 1861 to prolong the canal from Kassassin to the centre of the isthmus, and in the year 1863 they brought the fresh-water canal as far as Suez. In one or two places the bed of the old canal was cleared out and made to serve the new canal. The level of the fresh-water canal is about twenty feet above that of the Suez Canal, which it joins at Ismailia by means of two locks. The difference of level between it and the Red Sea is remedied by four locks constructed between Nefeesh and its terminus at Suez. Its average depth of water at high Nile is six feet, and at low Nile three feet. A canal from Bulak, near Cairo, passing by Heliopolis and Belbeys, and joining the Wady Canal a few miles east of Zagazig, restores the line of water communication between the Nile and the Red Sea as it existed perhaps in the time of Trajan, and certainly as it was in the time of the Caliph Omar. The improvement of this canal as a means of transit is local and external only.