The trade of the empire must have been very greatly promoted by the roads which Darius made through it in every direction. Merchandise passed from one end of the empire to another on paved roads, which were provided with excellent inns and secured by numerous guard-posts. Moreover, by his royal currency, Darius had created money which passed from the Hellespont and the Nile to the Indus, and thus the merchants had everywhere at hand a fixed measure of value. The raw products which were required by the manufacturing lands, could be bartered in safety, on the upper Nile, in Libya and Arabia, and on the Indus; the wide market which the extent of the Persian kingdom opened to the harbour cities of Asia Minor and Syria, to the industry of the Lydians and Phenicians, the Egyptians and Babylonians, could be used in the readiest and most profitable manner. Ramses II. of Egypt had conceived the idea of a direct communication by water between the Nile and the Red Sea in order to facilitate the trade with South Arabia. For this object he had caused a canal to be taken from the Nile at Bubastis, but he had only carried it as far as the Lake of Crocodiles. Pharaoh Necho more than 700 years later had again taken up the work and carried the canal as far as the Bitter Lakes. From this point the canal was to abandon the direction towards the east and turn almost at a right angle to the south and the Red Sea. Necho failed to effect the communication between the Bitter Lakes and the Red Sea; and the canal remained unfinished. Herodotus, who knew nothing of the attempt of Ramses II., says: "Darius carried a canal from the Nile to the Arabian Gulf."[396] "Necho was the first to attempt a canal leading into the Red Sea, and Darius accomplished what he began. The length of the voyage is four days, and the canal is broad enough to allow two triremes when rowing to pass one another (_i.e._ more than 100 feet). The water of the Nile flows into it a little above Bubastis, and empties into the Red Sea. For the first part it is excavated in the plain of Egypt, which lies towards Arabia, under the mountains opposite Memphis, in which are the stone quarries. At the foot of the mountain the canal runs away to the east, and then through a cleft in the range to the south, and southward, into the Arabian Gulf. The distance from the northern sea--the Mediterranean--to the Red Sea by the shortest route from Pelusium[397] is 1000 stades (105 miles); but the canal is much longer, owing to bends in it."[398] In the bed of this canal, the direction of which can still be traced in part, three stones were discovered at Saluf El Terraba, on the Crocodile Lake, not far from the southern ridge of the Bitter Lakes. They have recently been much injured by the workmen at the Suez canal. On the front is seen the form of Darius with the tall tiara on his head (the upper part of one of the monuments is preserved); and beside the figure of the king we find the name and title in hieroglyphics.