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 Indian subcontinent. Within two years, Alexander expanded the Macedonian Empire to include present-day Punjab and Sindh in what is Modern-day Pakistan, surpassing the earlier frontiers that had been established by the Persian conquest of the Indus Valley.
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. In 326 BC, Alexander defeated Porus and the Pauravas during the Battle of the Hydaspes, but that engagement was possibly their 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.
There are no ancient sources at all giving an Indian account of the campaign, or even mentioning it at all. There is no mention of Porus in the extremely sparse Indian accounts of the period. There are however Indian literary accounts and Indian folktales, possibly written many years later.
Of those who accompanied Alexander to India, Aristobulus, Onesicritus, and Nearchus wrote about the Indian campaign.