The Indian campaign of Alexander the Great began in 327 BC and lasted until 325 BC. After conquering the Achaemenid Persian Empire, the Macedonian army undertook an expedition into the northwestern Indian subcontinent. Within two years, Alexander the Great expanded the Macedonian Empire, a Hellenistic kingdom, to include Gandhara and the Indus Valley (present-day Punjab and Sindh), surpassing the earlier frontiers established by the Persian Achaemenid conquest.
Following annexation of Gandāra (a former Persian satrapy), Alexander and his troops advanced into Punjab, where he received submission of the king Omphis of the city of Taxila, and confronted Porus, another regional king. In 326 BC, Alexander defeated the Pauravas under Porus in the Battle of the Hydaspes, although the engagement was possibly the Macedonians' most costly battle.
Alexander's continued eastward march was leading his army into a confrontation with the Nanda Empire, based in Magadha. According to Greek sources, the Nanda army was five times the size of the Macedonian army; Alexander's troops — increasingly exhausted, homesick, and anxious by the prospects of having to further face large Indian armies throughout the Indo-Gangetic Plain — mutinied at the Hyphasis River, refusing to advance his push to the east. After a meeting with his army general Coenus, during which he was informed of his soldiers' laments, Alexander relented under the conviction that it was better to return. He subsequently turned southward, advancing through southern Punjab as well as Sindh, where he conquered more tribes along the lower areas of the Indus River, before finally turning westward to reach Macedon by crossing the hazardous Gedrosian desert.
Background
Sources
Of those who accompanied Alexander to India, Aristobulus, Onesicritus, and Nearchus wrote about the Indian campaign. The only surviving contemporary account of Alexander's Indian campaign is a report of the voyage of the naval commander Nearchus, who was tasked with exploring the coast between the Indus River and the Persian Gulf. This report is preserved in Arrian's Anabasis (c. 150 AD). Arrian provides a detailed account of Alexander's campaigns, based on the writings of Alexander's companions and courtiers.
Arrian's account is supplemented by the writings of other authors, whose works are also based on the accounts of Alexander's companions: these authors include Diodorus (c. 21 BC), Strabo (c. 23 AD), and Plutarch (c. 119 AD).
Socio-political conditions in India
Alexander's incursion into India took place primarily in the Indus River basin area, which was divided among several small states. These states appear to have been based on dominance of particular tribes, as the Greek writers mention tribes such as the Malloi as well as kings whose names seem to be tribal designations. The Achaemenid Empire of Persia had held suzerainty over the Indus valley in the previous decades, but there was no trace of Achaemenid rule beyond the Indus river when Alexander's army arrived in the region. Strabo, sourcing his information from the earlier writer Eratosthenes, states that the Achaemenid king controlled the area to the west of the Indus. 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.
Greek writings as well as archaeological excavations indicate the existence of an urban economy dependent on agriculture and trade in the Indus basin. The Greeks mention the existence of cities and fortified towns such as Taxila. Arrian mentions that after defeating Porus, Alexander marched eastwards towards the Chenab River, and captured 37 towns: the smallest of these towns had 5,000 or more inhabitants. In the Swat Valley, Alexander is said to have seized 230,000 oxen (possibly Zebu), intending to send them to Macedonia for ploughing land. 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). Nearchus also mentions that Indians wore clothes made of cotton. Rock salt was extracted from the Salt Range, and supplied to other parts of India. Some primitive communities existed in the forest, desert, and coastal regions of the subcontinent. For example, Nearchus mentions that people around the Tomeros river (Hingol) subsisted on fishing, and used stone tools instead of iron ones.
The Greek writers mention the priestly class of Brahmanas (as "Brachmanes"), who are described as teachers of Indian philosophy. They do not refer to the existence of any religious temples or idols in India, although such references commonly occur in their descriptions of Alexander's campaigns in Egypt, Mesopotamia and Iran. Greek accounts mention naked ascetics called gymnosophists. A philosopher named Calanus (probably a Greek transcription of the Indian name "Kalyana") accompanied Alexander to Persepolis, where he committed suicide on a public funeral pyre; he was probably a Jain or an Ajivika monk. There is no reference to Buddhism in the Greek accounts.
Other than their mention of the Brahmanas, the Greek narratives about Alexander's invasion do not directly mention the caste system. Some Brahmanas acted as advisors to local princes: Alexander had groups of Brahmanas hanged in present-day Sindh for instigating the rulers Musicanus and Sambus to revolt against him. The Greek writings attest the existence of slavery in at least two places: Onesicritus describes slavery in the territory ruled by Musicanus, and Aristobulus mentions poor people selling their daughters publicly in Taxila. Aristobulus also observed Sati, the practice of widows immolating themselves on their husbands' pyre, at Taxila. The practice of exposing dead bodies to vultures, similar to the Magian practice of Tower of Silence, was also prevalent in Taxila.
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. While describing a tribe on the coast of present-day Balochistan, Nearchus mentions that they were different from Indians in "their language and customs", which implies that he associated a particular language with the Indians. This does not mean that the Indians spoke a single language: the language that Nearchus associated with India might have been a lingua franca used for official and commercial purposes. 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").
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. The Greek accounts do not mention any other sciences of contemporary India.
Alexander's preparation
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. For Alexander, the invasion of India was a natural consequence of his subjugation of the Achaemenid Empire, as the areas of the Indus Valley had long been under Achaemenid control, since the Achaemenid conquest of the Indus Valley c. 515 BC. Alexander was only taking possession of territories which he had obtained from the Achaemenids, and now considered rightfully his own.
Alexander invited all the chieftains of the former satrapy of Gandāra, to come to him and submit to his authority. Omphis (Indic: Ambhi), ruler of Taxila, whose kingdom extended from the Indus to the Jhelum (Greek: Hydaspes), complied. 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.
Cophen campaign
In the satrapy of Gandāra, Alexander personally took command of the shield-bearing guards, foot-companions, archers, Agrianians, and horse-javelin-men and led them against the clans — the Aspasioi of Kunar Valley, the Guraeans of Panjkora Valley, and the Assakenoi of the Swat Valley.
Alexander faced resistance from Astis or Astes (Hasti), the chief of the Astakenoi or Astanenoi tribe, whose capital was Pushkalavati or Peukelaotis. Astes died defending his capital and Peucelaotis was annexed, with another local noble Sangaeus being appointed as satrap in his place. He later defeated the Aspasioi and captured their 40,000 men and 230,000 oxen; in the course of which Alexander himself was wounded in the shoulder by a dart, but eventually the Aspasioi lost the fight. Assakenoi of Massaga fought him under the command of their queen, Cleophis, with an army of 30,000 cavalry, 38,000 infantry, 30 elephants, and 7,000 mercenaries. Other regions that fought Alexander were Abhisara, Aornos, Bazira, and Ora or Dyrta.
The Assakenoi fought bravely and offered stubborn resistance to the invader in their strongholds. The fort of Massaga could only be reduced after several days of bloody fighting in which Alexander himself was wounded seriously in the ankle. When the chieftain of Massaga fell in the battle, the supreme command of the army went to his old mother, Cleophis, with women of the locality also going into war. Alexander was only able to reduce Massaga by resorting to political stratagem and actions of betrayal. According to Curtius: "Not only did Alexander slaughter the entire population of Massaga, but also did he reduce its buildings to rubbles". A similar slaughter then followed at Ora, another stronghold of the Assakenoi.
Siege of Aornos
In the aftermath of general slaughter and arson committed by Alexander at Massaga and Ora, numerous Assakenoi fled to a high fortress called Aornos (not definitely identified but somewhere in northern Pakistan). Alexander followed close behind their heels and besieged the strategic hill-fort. The siege of Aornos was Alexander's last siege, "the climax to Alexander's career as the greatest besieger in history", according to Robin Lane Fox. The siege took place in April 326 BC. 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 on a strongly reinforced mountain spur above the narrow gorges in a bend of the upper Indus. At the vulnerable north side leading to the fort, Alexander and his catapults were stopped by a deep ravine. To bring the siege engines within reach, an earthwork mound was constructed to bridge the ravine. A low hill connected to the nearest tip of Pir-Sar was soon within reach and taken. Alexander's troops were at first repelled by boulders rolled down from above. Three days of drumbeats marked the defenders' celebration of the initial repulse, followed by a surprise retreat. Hauling himself up the last rockface on a rope, Alexander cleared the summit, slaying some fugitives — inflated by Arrian to a massacre — and erected altars to Athena Nike, Athena of Victory, traces of which were identified by Aurel Stein. Sisikottus, or Saśigupta, who had helped Alexander in this campaign, was made the hyparch of Aornos.
Battle of the Hydaspes
After reducing Aornos, Alexander crossed the Indus to begin campaigning in the Punjab region. The main train went 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. In early spring of the next year, he combined his forces and allied with Taxiles (also Ambhi), the King of Taxila, against his neighbor, Porus. He also received submission of kings like Sophytes.
The Battle of the Hydaspes River was fought by Alexander in July 326 BC against king Porus (possibly king of Paurava) on Hydaspes (Jhelum River) in the Punjab, near Bhera. The Hydaspes was the last major battle fought by Alexander.
Arrian writes about Porus, in his own words:
One of the Indian Kings called Porus, a man remarkable alike for his personal strength and noble courage, on hearing the report about Alexander, began to prepare for the inevitable. Accordingly, when hostilities broke out, he ordered his army to attack Macedonians from whom he demanded their king, as if he was his private enemy. 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. The Jhelum was deep and fast enough that any opposed crossing would probably doom the entire attacking force. Alexander knew that a direct crossing would fail, so he found a suitable crossing, about 27 km (17 mi) upstream of his camp. The name of the place is "Kadee". Alexander left his general Craterus behind with most of the army while he crossed the river upstream with a strong contingent. Porus sent a small cavalry and chariot force under his son to the crossing.