Alexander the Great actually did invade India. But after marching 11,000 miles, his undefeated army finally mutinied over a terrifying rumor: 6,000 war elephants.
In 326 BC, the Macedonians had already crossed the Indus River into the Punjab region, scoring a tactical victory against King Porus at the Battle of the Hydaspes. However, when ordered to cross the Hyphasis (modern-day Beas) River and push deeper into the subcontinent, the veterans simply refused to take another step east.
Their mutiny was driven by compounding pressures. The soldiers were exhausted, homesick, and weary of endless campaigning. Furthermore, the army had arrived during the violent summer monsoon season. Seventy days of relentless rain turned the terrain into deep mud, ruining their supplies and exposing the men to unfamiliar diseases and venomous snakes.
The final breaking point was the intelligence brought back about the Nanda Empire of the Ganges basin. Scouts reported that the Nanda king, Dhana Nanda, was waiting for them with an army that dwarfed anything Alexander had faced: 200,000 infantry, 80,000 cavalry, and those thousands of war elephants.
The Greeks had barely survived fighting just 85 of Porus’s elephants at the Hydaspes, where the massive animals trampled their phalanx formations and caused severe casualties. The prospect of facing thousands of them shattered the army's morale. Coenus, one of Alexander's most trusted generals, pleaded with him on behalf of the men, arguing that it was time to return to Greece rather than press on to certain destruction.
Alexander was furious. He shut himself in his tent for three days, hoping his veterans would relent and follow him. When the army held its ground, he finally yielded. Before turning south to begin the brutal journey down the Indus River toward the sea, he ordered the construction of twelve massive stone altars on the riverbank—a permanent monument to mark the absolute easternmost limit of his empire.