Which river valley civilization was the largest?

The largest river valley civilization was the Indus Valley Civilization, which flourished around 2500 BCE in present-day Pakistan and northwest India. It covered a vast area, with major urban centers like Harappa and Mohenjo-Daro, and was characterized by advanced urban planning, sophisticated drainage systems, and a script that remains undeciphered. This civilization was notable for its impressive size and complexity, influencing later cultures in the region.