3. The Indus Valley Civilization
The Indus Valley Civilization, home to advanced cities like Harappa and Mohenjo-daro, flourished for centuries before its sudden decline around 1900 BCE. These urban centers were mysteriously abandoned, leaving behind sophisticated architecture and artifacts. Scholars debate the exact cause—some point to changing river patterns or catastrophic floods, while others suggest invasions or internal strife. The swift disappearance of this civilization remains an archaeological enigma. Discover more at National Geographic.
