The Indus River Valley civilization arose around 6500 BCE in what is now Pakistan and northwestern India. Two major cities, Harappa and Mohenjo-Daro, were home to over 50,000 people each and featured advanced architecture including defensive walls, well-planned streets, and sophisticated water and drainage systems. The Indus people cultivated wheat, barley and cotton and engaged in extensive trade. Though the civilization declined between 2000-1800 BCE for unknown reasons, it was highly advanced for its time period.