While the triremes were being built for him, and the harbour near Babylon was being excavated, Alexander sailed from Babylon down the Euphrates to what was called the river Pallacopas, which is distant from Babylon about 800 stades.[947] This Pallacopas is not a river rising from springs, but a canal cut from the Euphrates. For that river flowing from the Armenian mountains,[948] proceeds within its banks in the season of winter, because its water is scanty; but when the spring begins to make its appearance, and especially just before the summer solstice, it pours along with mighty stream and overflows its banks into the Assyrian country.[949] For at that season the snow upon the Armenian mountains melts and swells its water to a great degree; and as its stream flows high above the level of the country, it would flow over the land if some one had not furnished it with an outlet along the Pallacopas and turned it aside into the marshes and pools, which, beginning from this canal, extend as far as the country contiguous to Arabia. Thence it spreads out far and wide into a shallow lake, from which it falls into the sea by many invisible mouths. After the snow has melted, about the time of the setting of the Pleiades, the Euphrates flows with a small stream; but none the less the greater part of it discharges itself into the pools along the Pallacopas. Unless, therefore, some one had dammed up the Pallacopas again, so that the water might be turned back within the banks and carried down the channel of the river, it would have drained the Euphrates into itself, and consequently the Assyrian country would not be watered by it. But the outlet of the Euphrates into the Pallacopas was dammed up by the viceroy of Babylonia with great labour (although it was an easy matter to construct the outlet), because the ground in this region is slimy and most of it mud, so that when it has once received the water of the river it is not easy to turn it back. But more than 10,000 Assyrians were engaged in this labour even until the third month. When Alexander was informed of this, he was induced to confer a benefit upon the land of Assyria. He determined to shut up the outlet where the stream of the Euphrates was turned into the Pallacopas. When he had advanced about thirty stades, the earth appeared to be somewhat rocky, so that if it were cut through and a junction made with the old canal along the Pallacopas, on account of the hardness of the soil, it would not allow the water to percolate, and there would be no difficulty in turning it back at the appointed season. For this purpose he sailed to the Pallacopas, and then continued his voyage down that canal into the pools towards the country of the Arabs. There seeing a certain admirable site, he founded a city upon it and fortified it. In it he settled as many of the Grecian mercenaries as volunteered to remain, and such as were unfit for military service by reason of age or wounds. CHAPTER XXII.