With the Hydaspes in flood, there was, of course, no immediate possibility of fording the river. Alexander gave out publicly that he was content to wait for the autumn months when the water would run very much lower. No doubt he intended that such a pronouncement should come to the ears of the enemy but it is quite evident that he had laid other plans.
Porus strongly guarded all possible ferry crossings, and his elephants became extremely useful in this role, for they would certainly terrify any horses that confronted them, making a cavalry landing from rafts or barges quite impossible. But Alexander was, as ever, resourceful. Before moving up to the frontiers of Porus’ territory, he had dismantled the boats and galleys he had used on the Indus. The smaller craft had been broken into two parts, the 3o–oar galleys into three parts; the sections had then been transported on wagons overland and the whole flotilla reassembled on the Hydaspes. From the first, these boats had been able to navigate the river unmolested, the Indians having made no attempt to deny them the use of the midway channel.
During the weeks that followed, Alexander moved his cavalry continually up and down the river bank. Porus, to forestall the concentration of Alexander’s troops at any single point, dispatched forces to march level with Alexander’s men on the opposite bank, guided by the noise that the Macedonians were deliberately creating. Any place at which a crossing seemed contemplated was immediately guarded in strength by the Indians. Alexander’s movements were however, mere feints. No attack materialized and eventually Porus relaxed his vigilance. This, of course, was Alexander’s intention. The Macedonians were now in a position to make a real attack. Any sound of their movements would inevitably be discounted by the enemy as another false alert.
As they moved up and down the riverbank, Alexander’s cavalry had been reconnoitring for suitable crossing places, reporting back to Alexander. He now selected one, and made plans to cross the Hydaspes by night. He left his officer Craterus in the area where the Macedonian army had originally encamped, together with the cavalry unit this officer normally commanded, as well as attached units of Asiatic cavalry and local Indian troops to the number of 5,000, plus two units of the Macedonian phalanx.
Alexander himself set out for the chosen crossing place with a similarly mixed but stronger force. It included the vanguard of the Companion cavalry and the cavalry units of his officers Hephaestion, Perdiccas and Demetrius. These units were hipparchies of greater strength than the squadrons he had used in Asia Minor. He also led Asiatic troops that included mounted archers, and two phalanx units with archers and Agrianians.
The purpose of leaving a substantial force at the base camp was to disguise Alexander’s movements from Porus. It was imperative that the Indians knew nothing of the crossing until it was accomplished. His orders to Craterus were that if Porus led away only part of his army to meet this emergency, leaving a force of elephants behind him, then the Macedonians at the base camp should remain where they were, covering the enemy on the opposite bank. However, if Porus abandoned his position entirely, either in flight, or to face Alexander, then Craterus and his men might safely cross. In fact, the main danger to the Macedonian cavalry was from the elephants. Once these were withdrawn, the river might confidently be crossed, no matter what other Indian troops remained.
The point selected as a crossing place was about 18 miles upstream from the base camp. Here, on the opposite bank, was a headland where the river bent, covered with luxuriant undergrowth, and in the river alongside it rose the island of Admana, also densely forested and so providing concealment for the proximity or presence of cavalry. Along the Macedonian bank Alexander had already posted a chain of pickets, capable of communicating with each other either by visual or audible signals. Similar to his previous practice, Alexander had allowed the enemy to become accustomed to the shouts and nightly watchfires of these outposts.
Screened by such diversions, Alexander’s march was made in great secrecy. It followed an inland route, possibly a short cut. As the Macedonians marched through the night, they were overtaken by a thunderstorm and heavy rain. Though they cannot have enjoyed it, the storm must have rendered their movement imperceptible to the enemy.
At the crossing place a ferry fleet had been prepared in advance. Many of the ferries were rafts floated on skins that had been transported empty to the spot, then stuffed with chaff and sewn up to make them watertight. Alexander had previously used this technique for ferrying troops on the Danube and on the Oxus. Alongside these waited the 30-oar galleys carried overland from the Indus.
Close to the river bank, at an intermediate position between the base camp and the ferry point, he stationed three of his officers, Meleager, Attalus and Gorgias, each in charge of his own infantry unit, with attached cavalry and infantry detailed from the mercenaries. Like Craterus, this force was ordered to cross only when it saw that the enemy on the opposite bank of the river was committed elsewhere. The crossing was to be made in three waves, probably because there were not enough ferries to permit a transit in one body.
At dawn the storm subsided. As the ferry flotilla, led by Alexander and his staff in a galley, moved out into the river, it was initially out of sight of the opposite bank. But as they went further across the river they were obliged to break cover, and enemy scouts galloped off to report their approach.
Alexander’s men now ran into unforeseen difficulties, as the bank that had seemed to be the mainland opposite in reality belonged to another island. A deep but narrow channel separated it from the land beyond, and men and animals barely managed to ford the fast–flowing current – sometimes with little more than their heads above water. Emerging at last from this second crossing, Alexander was able to marshal his troops unmolested by the enemy and without difficulty on the opposite bank.