The ancient civilization that developed in the Indus Valley is known as the Indus Valley Civilization, also referred to as the Harappan Civilization. Flourishing around 2500 BCE, it was characterized by advanced urban planning, sophisticated drainage systems, and significant agricultural practices. Major cities included Harappa and Mohenjo-Daro, noted for their well-organized streets and architecture. The civilization is remarkable for its writing system, which remains undeciphered, and for its trade networks that extended across regions. The decline of the Indus Valley Civilization around 1900 BCE remains a subject of study, with theories suggesting climate change, invasion, or economic factors as possible causes.