This hard preliminary campaign lasted all the winter; in the spring the Indus was crossed and a three days’ march was made eastward to Taxila, a rich country, whose prince, along with lesser princes, gave a friendly welcome to the conqueror. But this friendly attitude was not taken by Porus, the ruler of the region farther south, who sent a formal defiance to Alexander, and prepared to resist the invaders by collecting an army of from thirty to forty thousand men. With this he encamped on the river Hydaspes and prepared to contest its passage. Alexander transported the boats, which he had constructed for crossing the Indus, to the Hydaspes, and took up a position on the right bank of the stream, near Jalalpur, in view of the army of Porus, who had collected a large number of elephants, a formidable obstacle to the effective use of the Greek cavalry. (326 B.C.) In the face of an enemy so placed the transit of the river was impossible, for the edge of the stream was slimy, making an insecure footing for the soldiers, and the horses, terrified by the presence of the elephants, could not be kept in control and would certainly be lost. Besides, Porus kept a sharp eye on all the fords near his camping ground. Alexander kept the enemy busy by making various feints as if he were about to attempt to pass the stream. It was the rainy season, and the Indian soldiers and elephants were kept in battle array at the threatened points, exposed for hours to the force of the wind and rain. Porus began to think that the Greeks were afraid to force the passage, and these manœuvers were continued until he was off his guard. Some sixteen miles below the Greek encampment, where the river made a bend, there was a wooded island which hid the right shore from observation. Taking advantage of this, and also of the fact that on his side of the river there was a thick forest, Alexander managed to bring his boats, which were made of skins, to a place opposite the island, and at the same time he marched some of his troops down the stream, leading them by a detour some distance from the bank, in order to prevent the enemy from detecting his operations. The rest of the Greeks were left at the original camping ground or were posted along the river at different points, with directions to cross and aid him at the proper moment.