Debated. New dating tests may place the first wall hundreds of years earlier than people used to think, but that older age is still not settled.
Mohenjo-daro stands by the Indus River in the Larkana district of Sindh, in Pakistan. Researchers studied a huge mud-brick wall around the western mound. The page says the lowest part was built about 2700 to 2600 BC, at the end of an early time called Kot Diji. Pots from that early time lay in the ground below the wall, so people lived there before the wall went up. The wall was built in more than one stage. Its upper part belongs to the time when the city was largest, from about 2600 BC, and the walls were looked after until at least 2200 BC. An earlier researcher thought the mud brick was only a barrier against floods. The new tests say it was a city wall.
People still argue about why the city was left empty between about 1800 and 1700 BC.