He crossed Sindhu and invaded India. Ambhi, the king of Taxila joined him here. Ambhi wished to defeat Porus king of Punjab with the help of Alexander. Porus and Alexander fought at the banks of Jhelum. Alexander's soldiers was overwhelmed by the elephants in Puru's army. This was a tough war, in which Puru was defeated by Alexander.
By this time, Alexander's army had exhausted. He started his retreat from India. On his way back he was attacked by the small kingdoms on the banks of Sindhu. On his way back, he died at Babylon at the age of 33.
With Alexander's invasion the Greek historians, philosophers came into India. From now on references to India were seen in official documents, which are authentic sources of Indian and Greek History.