In the plains of the Indus, which flooded twice a year, providing fertile grounds for abundent agriculture, the largest of the ancient civilizations resided, the IVC (3300 BCE - 1300 BCE).

They had great cities, like Mohenjo-daro and Harappa, perpendicular street, multi-story building, and written language (which we don't know how to read). In short, they were a developed society.

They even had a sewage and plumbing system.

Their biggest building was what is now known as the Great Bath.