On his return to Patala, he found the citadel fortified, and Peithôn arrived with his troops after completing the objects of his expedition. Hêphaistiôn was then ordered to prepare what was requisite for the fortification of the harbour, and the construction of a dockyard, for here at the city of Patala, which stands where the river Indus bifurcates, he meant to leave behind him a very considerable naval squadron. He himself sailed down again to the Great Sea by the other mouth of the Indus,[187] to ascertain by which of the mouths it was easier to reach the ocean. The mouths of the river Indus are about 1800 stadia distant from each other.[188] When he was approaching the mouth, he came to a large lake formed by the river in widening out, unless, indeed, this watery expanse be due to rivers which discharge their streams into it from the surrounding districts, and give it the appearance of a gulf of the sea;[189] for salt-water fish were now seen in it of larger size than the fish in our sea. Having anchored in the lake, at a place selected by the pilots, he left there most of the soldiers under the command of Leonnatos and all the boats, while he himself with the thirty-oared galleys, and the vessels with one and a half bank of oars passed beyond the mouth of the Indus, and sailing out into the sea by this other route, satisfied himself that the mouth of the Indus on this side was easier to navigate than the other. He then anchored his fleet near the beach, and taking with him some of the cavalry, proceeded along the shore a three days’ journey, examining what sort of a country it was for a coasting voyage, and ordering wells to be sunk for supplying sea-farers with water. He then returned to the fleet, and sailed back to Patala. He sent, however, a part of the army to complete the work of digging wells along the shore, with instructions to return to Patala on their completing this service. Sailing down again to the lake, he constructed there another harbour and other docks, and, having left a garrison in the place, he collected sufficient food to supply the army for four months, and made all other necessary preparations for the voyage along the coast. _Chapter XXI.—Alexander crosses the river Arabios and invades the Oreitai_