These aims seemed more plausible because of his faulty geography. India was believed to be bounded by the Eastern Ocean, a part of the waters which flowed round the Greeks' idea of the world, and though the facts were not yet certain, it did not sound as if the edge of India was impossibly far away. If the Eastern Sea was indeed Alexander's objective because it was the boundary of the world, then by playing each rajah off against his neighbour and crushing any resistance, Alexander could fight his way towards this thrilling end and crown his career with a sight which no Achilles had ever expected to sec. 'You, Zeus, hold Olympus; I set the earth beneath my sway.' Even if he was only marching east to explore and conquer India, an aim to which the world's end was incidental, the narrowed view of India and the false view of the Nile were still a strong encouragement; for wherever he marched, home, down the Indus-Nile, was always within reach. His ambitions were those of an explorer as much as a conqueror and only to men who have never shared in a search and a struggle against nature do these seem madness. But for the first time since the battle at Issus, Alexander was living under a bad mistake, and from the Chenab onwards, things began to go wrong.

The natives were numerous, though their weapons were old-fashioned: on the border of the Chenab alone Alexander forced thirty-seven cities and at least as many villages to surrender and added their half million citizens to Porus's kingdom. It was nothing new to the Macedonians to be outnumbered, but there were hazards which needed a stronger nerve. 'In India,' wrote Theophrastus the botanist, who had heard the survivor's reports and is too astute to be disbelieved, *the/Macedonians ate a type of wheat which was so powerful that many actually burst apart.' Such insights into their hardships are all too few; the only convincing figures for casualties are on an occasion when Alexander was not present. But this one at least has the merit of being unforgettable. Others ate from a tree 'which was not particularly large but had pods like a bean, ten inches long and as sweet as honey'; this, the Greeks' first meeting with a banana or perhaps a mango, gave them such upset stomachs that Alexander forbade them to touch it, 'and you were unlikely to survive', wrote Aristobulus, 'if you ate one' against his orders. Other trees were safer, if no less alarming: by the river Chenab the troopers marvelled at the banyan, the wonder of Indian dendrologists. 'The shoots of a single tree spread out into a huge shaded arbour, like a tent with many pillars,' so wide that 'fifty horsemen could shelter from the midday sun beneath it.' Close inspection showed that each separate 'trunk' was a giant shoot from one and the same root system, while the fruits were small but deliciously juicy. Farther east, there were to be reports of a banyan which cast a shadow for half a mile, by no means an impossibility: the prize banyan of the Calcutta Botanic Garden resembles a huge wood, four acres big and a quarter of a mile in circumference.

Even a banyan was at the mercy of the weather. As the Chenab came in view, midsummer made way for the monsoon proper to begin, and at last the army understood why the local villages had been built on banks and mounds. As the rain teemed down, the river rose from its bed and came to life as if roused from a long and reluctant sleep. The nullahs began to flood and the ditches could no longer take their overflow. Camp had to be hastily moved as the current rose, ten feet, twenty feet, thirty feet, until it burst its banks in disdain for the invaders. The men retired to the villages and watched the water race across the plains, in places even deeper than the elephants, and as they watched, they became aware of a threat which could not be so easily avoided: the floods had caused their houses to be plagued with snakes.

'Their numbers and their ferocity,' wrote Nearchus, 'were very surprising: at the time of the rains, they retreat to the higher villages and the natives therefore build their beds well above the ground, though even then, they are often forced to abandon their homes by this overwhelming invasion.' Species of python as long as twenty-four feet came in search of a dry comer: others were too tiny to be noticed, but it was these smaller snakes, scorpions and cobras who brought the most discomfort. 'They hid in the tents, the cooking-pots, the hedges and the walls: those whom they bit bled from every pore and suffered agony, dying very rapidly unless help was found in the drugs and roots of the Indian snake-charmers,' whose skill, however, was remarkably effective. Medical supplies were summoned urgently from all quarters, while wherever possible the men hung hammocks between the trees and spent an anxious night above the ground. Only by crossing the Chenab could they hope for better things.

But the Chenab was foaming and roaring in its mile-and-a-half-wide channel. Though Alexander chose the broadest and smoothest stretch for the crossing, even Ptolemy admitted that many of those who crossed by boat, rather than by rafts of stuffed leather, were dashed against the rocks so that 'not a few were lost in the water'. Once on the far bank Hephaistion was sent to deal with Indians to the north, while Porus returned to recruit as many elephants as possible, a sign that Alexander was expecting heavy fighting. Supplies were to be convoyed eastwards as soon as the river allowed, and in the meantime, he would live off the land.

Marching eastwards he waded across the river Ravi with his lightest troops and received the surrender of its nearest tribesmen. They told him of a tribe called the Cathaioi in the plains near Lahore who were bellicose by nature; they were said to have planned resistance and inflamed the tribesmen south on the Indus. Alexander hurried down to their territory in three days' rapid marching, with only one day for rest, and arrived at Sangala, their largest fortress. The Cathaioi had drawn up a triple line of carts off which they could defend themselves; cavalry failed to provoke them down from their hill, so the infantry line pushed in amongst them and drove them back behind Sangala's solid brick wall. Alexander had no siege machinery and could only encircle the fort while tunnels were dug to undermine it; a night escape was anticipated and cost the Indians five hundred lives. Just when the tunnels were being completed, Porus arrived with 5,000 Indian volunteers and the siege engines, a credit to the transport section who had hauled them across the mud of a summer monsoon. The engines were not needed, as the sapper's job had already sufficed; the wall subsided into the tunnel, ladders were slung across the breaches and brave resistance did not save 17,000 Indians from being slaughtered, according to Ptolemy, and another 70,000 being captured. 'Less than a hundred of Alexander's troops died in the siege' but more than 1,200 were wounded, an unusually high proportion for Ptolemy to admit and one which included many officers. The wounded were another bad burden on morale, and all the while the thunder rumbled and the rain poured down on weary men.

Neighbouring tribesmen were pursued to the death if they ran away, pardoned if they surrendered; Alexander 'would not be harsh to them if they stayed and received him as a friend, any more than he had been harsh to other self-governing Indians who surrendered willingly'. The continued stress on their 'ancient self-government' was a thin, but revealing, cloak for the campaign; momentarily, matters improved when the army reached Sopeithes's kingdom near Lahore and the river Beas.

When their engines of war drew near its capital city, out marched the native king, a tall figure dressed in gold and purple embroidery, golden sandals and bracelets and necklaces of pearl. He handed over his sceptre, studded with precious beryl, whereupon historians repaid his compliment: