[3] A previous king of the Persian Achaemenid Empire, Darius the Great, had sent one of his generals, Skylax, to sail down the Indus.

[4] Following this expedition, Darius was able to conquer the surrounding Indian territory and receive tribute of 350 Euboic talents per annum.

Returning to Alexandria ad Caucasum in May 327 BC[1] he found a surfeit of victual and supplies ready for the army for its expedition into India.

[8][12] Leaving Alexandria ad Caucasum, Alexander marched to Nicaea, where he sacrificed to Athena (which was his habit at the beginning of every campaign) and exclaiming that he was following in the footsteps of his ancestor Heracles, began his advance towards the Indus along the Cophen River.

[14][17] Their instructions were to follow the river to the Indus bringing all the cities and fortifications to submission on the way through either systematic reduction or by terms.

[19][16] Alexander's plan was to march along all the valleys that were in between Nicaea and the river Indus with the aim of subduing those tribes that had not paid tribute.

[22] Alexander then left Craterus, whom he had probably kept in hand in case of just such an occasion, in command of a force responsible for gaining and keeping control of the tribes living in the surrounding valleys.

[19][24] After defeating the Aspasians and thus securing his lines of communication, the Macedonians marched towards the Guraean fortified city of Arigaeum.

[25] The Guraeans had retreated after burning their fortified city, joined up with their fellow tribesmen and prepared themselves to face Alexander.

Ptolemy, who had been sent ahead on a foraging expedition,[25] came back to the main contingent of the army under Alexander and reported that there was a very large force assembled and preparing to face the Macedonians.

[25] When the Macedonians arrived where the assembled force had gathered, Alexander divided his army into three parts with Ptolemy taking up the left (he commanded a third of the hypaspists, the brigades of Philip and Philotas, two squadrons of horse archers, the Agrianians and half the remaining cavalry).

[26] As expected, the Guraeans attacked Alexander's small contingent and after Ptolemy faced rough fighting,[26] he was able to achieve victory on his flank.

[27] Following his victory over the Guraeans, Alexander marched down the Garaeus river subduing the tribes of this region to tribute paying status.

[28] Alexander raced forward with the van, trying to do all he could to upset their preparations, while Craterus followed up at a more methodical pace with the main force.

[27] The speed with which the Macedonian van proceeded was such that Alexander was able to prevent facing a full complement of enemy forces.

"[30] A subsequent assault on Massaga proved to be unsuccessful[31] with the professional mercenaries showing that they were worth the gold they were getting paid.

[30] Archers and slingers, most likely from Cyprus, were stationed on the tower as it was moved forward in order to keep the defenders at a distance.

[32] When it became clear that the stronghold would surrender,[32] Alexander decided to dispatch a number of his lieutenants to the surrounding fortress towns to follow up on this victory.

[34] However, while proceeding to Bazira he received the news that Abisares, the ruler of Hazara, was going to cross the Indus[35] with his soldiers to interrupt the siege and assist Ora.

[34] In addition to this, he ordered Coenus to establish a camp and fortify it as an eventual base of operations against the town of Bazira.

[34] Coenus was then to leave a suitable garrison at that base to observe Bazira and while he joined Alexander and his forces at Ora.

Once he had consolidated his hold there and made his arrangements for crossing the Indus quite secure, he could safely move up to the right bank and attack the mountain retreat of the Swat fugitives from the south.

The fugitive host could be cut off from retreat to the east of the Indus and from such assistance as Abisares, the ruler on that side, might offer.

It offered the last threat to Alexander's supply line, which stretched in a dangerously vulnerable manner, over the Hindu Kush back to Balkh.

The site lies north of Attock in Punjab, on a strongly reinforced mountain spur above the narrow gorges in a bend of the upper Indus River.

Ptolemy and Alexander's secretary Eumenes, whose account provided material for all later records of the event, reconnoitred and reinforced a neighbouring spur to the west with a stockade and ditch.

To bring the siege engines within reach, an earthwork mound was constructed to bridge the ravine with carpentry, brush and earth.

The first day's work brought the siege mound 50 metres (60 yards) closer, but as the sides of the ravine fell away steeply below, progress rapidly slowed.

Nevertheless, at the end of the third day, a low hill connected to the nearest tip of Pir-Sar was within reach and was taken, after Alexander in the vanguard and his first force were repelled by boulders rolled down from above.

[40][41][42] Then, together with his Companion cavalry went to the mountain and they made ivy garlands and crowned themselves with them, as they were, singing hymns in honor of Dionysus.