This is a grey area of history. While the Porus-Alexander story is legendary, there is no guarantee that it actually took place. Neither is there any guarantee that it did not. And there the matter lies as on date.
The Alexander episode does not find much mention in the entire written record, that is the strangest aspect of it. Neither is there any record of the presence of any King called Porus in North-Western India during that time. There are very few references in Indian records, which is a very curious and noteworthy aspect of this matter. The closest one comes to it is the Puru Tribe of Northwest India. Beyond that, there is little evidence. Remember that initial history was written by Europeans; a few of these initial writings are beginning to be challenged as new evidence emerges. There are quite a few gaps in the accepted records; even for established figures like Ashok. In Ashok's case, the narrative throws up significant differences in the approach of The Ashokavadaan and the other books from that time: like the Mahavamsa. The 2 simply do not reconcile in most of the important details of the emperor's life. Similar is the case of Alexander. The only thing that is certain is that the supposed invasion does not merit a detailed coverage in any Indian records from that day.
In 327 BC Alexander, in his march against Emperor Darius empire, came into India.This lasted for 2 years. There is no record in Indian sources of his exploits, and there was little consequence of his invasion in the long term. He came to India to reach the easternmost parts of Darius' empire - reach the ocean. This ran into trouble along the Sindhu river (Indus), and he then went along the river, fighting many battles - Puru, subduing of the Gana-Sanghas, Battle with the Malloi where he was injured - and exacted a brutal revenge.
He is supposed to have built an alliance with Ambhi of Taxila, and attacked Puru on the banks of the Jhelum. One historical source even claims that the name Puru may have been referring to the Puru Tribe, which has inhabited the area since Rug-vedic times. Alexanders' invasion is not mentioned in any Indian Texts; we only have Macedonian records, No one can say for sure how accurate they are. Some of them state the presence of giant ants that dig for Gold! Sample this observation:
There are men said to be 10 feet tall and six feet wide; some had ears reaching down to their feet - Megasthenes in Ancient India as described by Megasthenes and Arrian. This does not mean all of their observations were hogwash, some were accurate. They are supposed to be a mix of fact and fable.
In all history texts that I have read (please dont refer online or western sources for this) the entire Puru episode does not include more than 4 lines. There is no guarantee of the accuracy of that episode. That battle did take place is about the only thing that is certain; as is the fact that Alexander won. As to the rest - could be conjecture, or could be fact, No Idea.
The most important result of Alexander's exploits is sadly forgotten - the emergence of the Mourya Dynasty... but that is another story
Ref: Early India - Romila Thapar; Land Of The Seven Rivers- Sanjeev Sanyal
Alexander did not return after defeating Porus (or the puru tribe); he went further along the river. He was actually injured in the battle against the Malloi; not against Porus. He did decide to turn back after the Puru battle, but he instead went further along the river, thinking that this is the river Nile. They discovered their mistake on reaching the ocean, and then subsequently turned along the Makran and Persian Gulf coast.
That is all that is known - all from Greek records. None from Indian records; which are silent on this, which is very curious indeed.
First answered here: http://qr.ae/NCnTd