The work of Necho was continued by Darius, the son of Hystaspes (520 B.C.). The natural channel of communication between the Heroopolite Gulf and the Red Sea had begun to fill up with silt even in the time of Necho, and a hundred years later, in the time of Darius, was completely blocked, so that it had to be entirely cleaned out to render it navigable. The traces of this canal can still be plainly seen in the neighbourhood of Shaluf, near the south end of the Bitter Lakes. The present fresh-water canal was also made to follow its course for some distance between that point and Suez. Persian monuments have been found by Lepsius in the neighbourhood, commemorating the work of Darius. On one of these the name of Darius is written in the Persian cuneiform characters, and on a cartouche in the Egyptian form. Until this date it therefore appears that ships sailed up the Pelusiac branch of the Nile to Bubastis, and thence along the canal to Heroopolis, where the cargoes were transhipped to the Red Sea. This inconvenient transfer of cargoes was remedied by the next Egyptian sovereign, who bestowed much care on the water connection between the two seas. Ptolemy Philadelphus (285 B.C.), in addition to cleaning out and thoroughly restoring the two canals, joined the fresh-water canal with the Heroopolite Gulf by means of a lock and sluices, which permitted the passage of vessels, and were effective in preventing the salt water from mingling with the fresh water. At the point where the canal joined the Heroopolite Gulf to the Red Sea, Ptolemy founded the town of Arsinoe, a little to the north of the modern Suez. The line of communication between the two seas was impassable during the reign of Cleopatra (31 b.c.). It is believed by some that it was restored during the reign of the Roman emperor Trajan (98-117). During this period the Pelusiac branch of the Nile was very low, the water having almost completely deserted this formerly well-filled course. If Trajan, therefore, undertook to reopen the water way, he must have tapped the Nile much higher up, in order to reach a plentiful supply of water. The old canal near Cairo, which elsewhere joined the line of the former canal on the way to the Bitter Lakes, was once called "Amnis Trajanus," and from this it has been inferred that Trajan was really the builder, and that during his reign this canal was cleaned and rendered navigable. As there is no further evidence than the name to prove that Trajan undertook so important an enterprise, the "Amnis Trajanus" was probably constructed during the Arabic period.