Alexander the Great crossed into India in 327 BC and the greatest of Alexander's battles in India was against Porus at the Hydaspes River in 326 BC. Porus was defeated in a fierce battle. Alexander's next goal was to reach the Ganges
but his commanders refused to go further east as they had heard tales of the powerful Indian tribes that lived on the Ganges and also remembering the difficulties, they faced against Porus. So they decided to travel south down the Indus River. Alexander and his army reached the mouth of the Indus
in July 325 BC and from here, they returned home. With this came the end of the first phase of Greeks in India.
In 206 BC, a Seleucid king of Mediterranean defeated an Indian king Subhagasena and this revealed that the north-west of India was unguarded. Demetrius, the king of Bactria, followed the footsteps of Alexander through the Kyber Pass and extended his power into the northern Indus Valley. Here he began what was to become a series of wars between the Greeks and Indians. And this started the second phase of Greek rule in India and a long lineage of Indo-Greek rulers ruled over the western parts of the sub-continent.
Between the years 155 BC and 130 BC,
Menander ruled in India's northwest. He sent his army into the Ganges Valley as far as Magadha's capital, Pataliputra. But he failed to capture Magadha. Menander converted to Buddhism. This conversion facilitated the passage of Buddhist ideas west.
From 141 to 128 BC the Greeks, who were already weakened by warfare, was attacked by Scythians several times. The last of the Greek kings in India, Hermaeus, tried unsuccessfully to defend his rule from these attacks. The Greeks, Scythians and Parthians fought several battles in the first century BC in the Indus Valley. The Scythians emerged successful and ended Greek rule in India but maintained the Indo-Greek culture.
The Greeks brought with them a better coin than was being used in India, which contributed to regional and inter-regional trade. They brought with them ideas in astronomy, architecture and art that spread through India, and with the new art came new depictions of Hindu gods and a new image of the Buddha.