In 327 BCE Alexander the Great began his foray into Punjab. King Ambhi, ruler of Taxila, surrendered the city to Alexander. Many people had fled to a high fortress/rock called Aornos.
Aornos was taken by Alexander by storm after a successful siege. Alexander fought an epic battle against the Indian monarch Porus in the Battle of Hydaspes (326). After victory, Alexander made an alliance with Porus and appointed him as satrap of his own kingdom. Alexander continued on to conquer all the headwaters of the Indus River.
East of Porus’ kingdom, near the Ganges River, was the powerful kingdom of Magadha, under the Nanda Dynasty.
According to Plutarch, at the time of Alexander’s Battle of the Hydaspes River, the size of the Magadha’s army further east numbered 200,000 infantry, 80,000 cavalry, 8,000 chariots, and 6,000 war elephants, which was discouraging for Alexander’s men and stayed their further progress into India:
“ As for the Macedonians, however, their struggle with Porus blunted their courage and stayed their further advance into India. For having had all they could do to repulse an enemy who mustered only twenty thousand infantry and two thousand horse, they violently opposed Alexander when he insisted on crossing the river Ganges also, the width of which, as they learned, was •thirty-two furlongs, its depth •a hundred fathoms, while its banks on the further side were covered with multitudes of men-at‑arms and horsemen and elephants. For they were told that the kings of the Ganderites and Praesii were awaiting them with eighty thousand horsemen, two hundred thousand footmen, eight thousand chariots, and six thousand fighting elephants. And there was no boasting in these reports. For Androcottus, who reigned there not long afterwards, made a present to Seleucus of five hundred elephants, and with an army of six hundred thousand men overran and subdued all India. ”
–Plutarch, Parallel Lives, “Life of Alexander”
Exhausted and frightened by the prospect of facing another giant Indian army at the Ganges River, his army mutinied at the Hyphasis (modern Beas), refusing to march further East. Alexander, after the meeting with his officer Coenus, was convinced that it was better to return.
Alexander was forced to turn south, conquering his way down the Indus to the Indian Ocean. He sent much of his army to Carmania (modern southern Iran) with his general Craterus, and commissioned a fleet to explore the Persian Gulf shore under his admiral Nearchus, while he led the rest of his forces back to Persia by the southern route through the Gedrosia (modern Makran in southern Pakistan).
Alexander left behind Greek forces which established themselves in the city of Taxila, now in Pakistan. Several generals, such as Eudemus and Peithon governed the newly established province until around 316 BCE. One of them, Sophytes (305–294 BCE), was an independent Greek prince in the Punjab.