Following Macedon's absorption of Gandhara (a former Persian satrapy), including the city of Taxila, Alexander and his troops advanced into Punjab, where they were confronted by Porus, the regional Indian king.

[6] The only surviving contemporary account of Alexander's Indian campaign is a report of the voyage of the naval commander Nearchus,[7] who was tasked with exploring the coast between the Indus River and the Persian Gulf.

[8] Alexander's incursion into India took place primarily in the Indus River basin area, which was divided among several small states.

[9] Strabo, sourcing his information from the earlier writer Eratosthenes, states that the Achaemenid king controlled the area to the west of the Indus.

[10] This area (including the Kapisa-Gandhara region) was probably the territory of the Indians, who according to the Greek accounts, fought alongside their overlord Darius III at the Battle of Gaugamela.

[11] Greek writings as well as archaeological excavations indicate the existence of an urban economy dependent on agriculture and trade in the Indus basin.

[7] Aristobulus saw rice being grown in paddy fields, Onesicritus reported the existence of a crop called bosmoran (possibly the pearl millet), and Nearchus wrote of "honey-yielding reeds" (presumably the sugarcane).

[13] Nearchus mentions that Indians wrote letters on closely woven cloth; it is possible that this is a reference to a precursor of the Kharoshthi script, which may have developed from the Aramaic alphabet during the Achaemenid rule.

This lingua franca was most probably the Gandhari Prakrit, as the Greek names (e.g. "Taxila" and "Sandrokottus") for Indian people and places seem to be derived from this language (e.g. "Takhasila" and "Chandagutta") rather than Sanskrit (e.g. "Takshashila" and "Chandragupta").

[14] Nearchus attests the existence of medical science in India: he mentions that when the Greek physicians failed to provide remedies for snake-bites to Alexander, the king gathered Indian healers who were also able to cure other diseases and painful conditions.

[14] After the death of Spitamenes and his marriage to Roxana (Raoxshna in Old Iranian) in 326 BC to cement his relations with his new Central Asian satrapies, Alexander was finally free to turn his attention to India.

At the end of the spring of 327 BC, Alexander started on his Indian expedition leaving Amyntas behind with 3,500 horse and 10,000 foot soldiers to hold the land of the Bactrians.

[citation needed] Alexander faced resistance from Hastin (or Astes), chief of the Ilastinayana (called the Astakenoi or Astanenoi) tribe, whose capital was Pushkalavati or Peukelaotis.

When the Chieftain of Massaga fell in the battle, the supreme command of the army went to his old mother, Cleophis, who also stood determined to defend her motherland to the last extremity.

In the aftermath of general slaughter and arson committed by Alexander at Massaga and Ora, numerous Assakenians fled to a high fortress called Aornos (not definitely identified but somewhere between Shangla, in Swat, and the Kohistan region, both in northern Pakistan).

[27] It presented the last threat to Alexander's supply line, which stretched, dangerously vulnerable, over the Hindu Kush back to Balkh, though Arrian credits Alexander's heroic desire to outdo his kinsman Heracles, who allegedly had proved unable to take the place Pir-Sar, which the Greeks called Aornis.

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

[30] The main train went into what is now modern-day Pakistan through the Khyber Pass, but a smaller force under the personal command of Alexander went via the northern route, resulting in the Siege of Aornos along the way.

Alexander lost no time in joining battle, but his horse being wounded in the first charge, he fell headlong to the ground, and was saved by his attendants who hastened up to his assistance.Porus drew up on the south bank of the Jhelum River, and was set to repel any crossings.

Diodorus wrote about the battle tactics of war elephants:Upon this the elephants, applying to good use their prodigious size and strength, killed some of the enemy by trampling under their feet, and crushing their armour and their bones, while upon other they inflicted a terrible death, for they first lifted them aloft with their trunks, which they twisted round their bodies and then dashed them down with great violence to the ground.

This they rest upon the ground, and pressing against it with their left foot thus discharges the arrow, having drawn the string far backwards for the shaft they use is little short for three yards long, and there is nothing can resist an Indian archer's shot, neither shield nor breast plate, nor any stronger defence if such there be.

Texile rode up as near as he dared and requested him to stop his elephant and hear what message Alexander sent him, escape was no longer possible.

Alexander, however, far from resenting this treatment of his messenger, sent a number of others, last of whom was Indian named Meroes, a man he had been told had long been Porus' friend.

[28] According to Plutarch this was one of Alexander's hardest battles:The combat then was of a more mixed kind; but maintained with such obstinacy, that it was not decided till the eighth hour of the day.

Plutarch also wrote that the bitter fighting of the Hydaspes made Alexander's men hesitant to continue on with the conquest of India, considering that they would potentially face far larger armies than those of Porus if they were to cross the Ganges River.

The elephant had gold rings around its tusks and an inscription was on them written in Greek: "Alexander the son of Zeus dedicates Ajax to Helios" (ΑΛΕΞΑΝΔΡΟΣ Ο ΔΙΟΣ ΤΟΝ ΑΙΑΝΤΑ ΤΩΙ ΗΛΙΩΙ).

[28] After crossing the River Chenab, Alexander joined by Porus with elephants and 5,000 local troops, laid siege to Sagala, where the Cathaeans (related to Kāṭhī)[34] had entrenched themselves.

Thus Alexander the Macedonian, after conquering all Asia, did not make war upon the Gangaridai, as he did on all others; for when he had arrived with all his troops at the river Ganges, he abandoned as hopeless an invasion of the Gangaridai when he learned that they possessed four thousand elephants well trained and equipped for war.Alexander, using the incorrect maps of the Greeks, thought that the world ended a mere 1,000 kilometres (620 mi) away, at the edge of India.

He therefore spoke to his army and tried to persuade them to march further into India, but Coenus pleaded with him to change his mind and return, saying the men "longed to again see their parents, their wives and children, their homeland".

[31] His forces, believing their king dead, took the citadel and unleashed their fury on the Malli who had taken refuge within it, perpetrating a massacre, sparing no man, woman or child.