Decline of the Indus Valley and the Aryan Migration

Around 1500 BCE, as the Indus Valley Civilization entered its final decline — likely caused by climate change, shifting river courses (the Saraswati dried up), and possibly tectonic events — Indo-Aryan-speaking peoples migrated into the Indian subcontinent through the northwestern mountain passes. They brought with them the Rigveda (composed ~1500–1200 BCE), the Sanskrit language, horse-drawn chariots, fire rituals, and a social hierarchy that would evolve into the caste system. The "Aryan invasion" theory of the 19th century has been largely replaced by the "Aryan migration" model, supported by genetic evidence showing steppe-related ancestry mixing with local populations. The encounter between the incoming Vedic culture and the indigenous Dravidian and tribal cultures of the subcontinent produced one of history's most consequential cultural syntheses — the foundation of what we now call Indian civilization.