The Indus Valley Civilization, one of the earliest urban civilizations, existed from around 3300 BC to 1300 BC in South Asia, notably in present-day India, Pakistan, and Afghanistan, starting its peak around 2500 BC. Major cities such as Harappa and Mohenjo-Daro showcased advanced urban planning and a strong agricultural economy, primarily focused on cotton production and trade. The civilization eventually declined due to a possible natural calamity, giving rise to subsequent cultures such as the Aryans, who established a caste system and contributed to literary works like the Mahabharata and Ramayana.