The Indus Valley or Harappan civilization was one of the earliest civilizations in South Asia, reaching its peak around 2500-1900 BCE. It was centered around the Indus River valley in modern-day Pakistan and northwest India. Major cities included Harappa and Mohenjo-Daro, which featured planned streets laid out in grids and sophisticated water and drainage systems. The Harappans engaged in agriculture as well as crafts and trade. Over time the civilization began to decline, possibly due to environmental changes or invasions, and had disappeared by around 1700 BCE.