The Indus Valley Civilization was an ancient civilization located in Northwestern India and Pakistan along the Indus River. It was one of the largest ancient civilizations, covering over 1 million square kilometers, with major cities like Harappa and Mohenjo-Daro housing up to 80,000 people each. The civilization had advanced urban planning with standardized brick architecture and drainage systems. They practiced agriculture including wheat, barley and cotton. While the writing system remains undeciphered, artifacts provide evidence of a sophisticated culture with organized cities, skilled craftspeople, and long-distance trade networks. The decline of the civilization around 1900 BC may have been due to ecological disturbances, natural disasters, or invasions.