It must be recollected that Diodorus wrote about four hundred years after Herodotus; and his information concerning the earlier events, from want of precision, appears to be deficient in accuracy. These two passages make it evident that Nekos had commenced some great improvements on the canal of Sesostris; and it appears to have been his intention to have made use of it in order to secure a naval superiority in the Red Sea. It is plain, too, from the statement of Herodotus, that Darius had completed the canal, in so far as that was possible, without the invention of locks, for forming an immediate communication with the Red Sea. And from the account of Diodorus, it seems that he viewed the canal of Darius, which for ages had served for a commercial route, as incomplete; because the actual junction of the waters of the canal and the Red Sea had not taken place until Ptolemy Philadelphus, by applying the invention of locks, had enabled vessels to quit the canal in order to navigate the sea. Strabo, who was also well acquainted with Egypt, from personal residence, mentions the locks constructed by Ptolemy. After saying that even Darius had left the junction of the canal with the Red Sea incomplete, from the danger of inundating the country, he adds--"During the government of the Ptolemies, the isthmus was cut through, and a closed passage (a _euripus_) formed, so that a ship, whenever it was required, could enter the outer sea or pass into the canal."[1] [1] Strabo, xvii. c. 1. Vol. iii. p. 444.--Ed. Tauch. Though the canal constructed by Darius had been in general use for commercial purposes, and was regarded by Herodotus, when he visited Egypt, as a work in every way complete, still there can be no doubt that its importance would be greatly increased by the locks connecting it with the Red Sea. The augmentation in the trade, and the improvement in the class of vessels which navigated the canal, induced Ptolemy to make the changes in the whole course, from which it received the name of the river of Ptolemy. A very great addition was thus made to the prosperity of Egypt, as the canal would remain navigable for four months annually, from the end of August to the end of December. During this season of the year, the people of the Delta had little to attend to but the exportation of their surplus produce, and clearing their granaries for a new harvest, by selling all that portion of their grain which was neither required for seed nor for the maintenance of their families.