Alexander crossed the Hindu Kush to enter the Indian subcontinent. This formidable mountain system formed the high-altitude gateway between Central Asia and the regions of Afghanistan and northern India that Alexander sought to conquer.
The crossing took place during Alexander's eastern campaigns in 327 BC, after he had consolidated much of the former Achaemenid Persian Empire. His army moved through difficult terrain, including routes associated with the modern Khyber region, before advancing toward the Indus Valley.
The Hindu Kush is often confused with the Himalayas because both are major Asian mountain systems. They are geographically connected but distinct: the Hindu Kush lies mainly in Afghanistan and northern Pakistan, while the Himalayas extend farther east along the northern edge of the Indian subcontinent. Alexander's route also involved other ranges and passes, but the Hindu Kush is the canonical answer to this question.