Mohenjo-daro belonged to the Indus civilization. Its neighborhoods, brick buildings, and drains demonstrate ancient urban organization, and the site also preserves a large bathing structure.
The writing system has no widely accepted complete decipherment. Researchers therefore rely more heavily on buildings, objects, and environmental evidence to interpret social life.
Architecture and urban infrastructure
Mohenjo-daro has a planned layout with rectilinear buildings arranged on a grid plan. Most were built of fired and mortared brick; some incorporated sun-dried mud-brick and wooden superstructures. The covered area of Mohenjo-daro is estimated at 300 hectares. The Oxford Handbook of Cities in World History offers a "weak" estimate of a peak population of around 40,000.
The sheer size of the city, and its provision of public buildings and facilities, suggests a high level of social organisation. The city is divided into two parts, the so-called Citadel and the Lower City. The Citadel – a mud-brick mound around 12 metres (39 ft) high – is known to have supported public baths, a large residential structure designed to house about 5,000 citizens, and two large assembly halls. The city had a central marketplace, with a large central well. Individual households or groups of households obtained their water from smaller wells. Waste water was channeled to covered drains that lined the major streets. Some houses, presumably those of more prestigious inhabitants, include rooms that appear to have been set aside for bathing, and one building had an underground furnace (known as a hypocaust), possibly for heated bathing. Most houses had inner courtyards, with doors that opened onto side-lanes. Some buildings had two stories.
Water supply and wells
The location of Mohenjo-daro was built in a relatively short period of time, with the water supply system and wells being some of the first planned constructions. With the excavations done so far, over 700 wells are present at Mohenjo-daro, alongside drainage and bathing systems. This number is unheard of when compared to other civilisations at the time, such as Egypt or Mesopotamia, and the quantity of wells transcribes as one well for every three houses. Because of the large number of wells, it is believed that the inhabitants relied solely on annual rainfall, as well as the Indus River's course remaining close to the site, alongside the wells providing water for long periods of time in the case of the city coming under siege.
Due to the period in which these wells were built and used, it is likely that the circular brick well design used at this and many other Harappan sites are an invention that should be credited to the Indus civilisation, as there is no existing evidence of this design from Mesopotamia or Egypt at this time, and even later. Sewage and waste water for buildings at the site were disposed of via a centralized drainage system that ran alongside the site's streets. These drains that ran alongside the road were effective at allowing most human waste and sewage to be disposed of as the drains most likely took the waste toward the Indus River.
Flooding and rebuilding
The city also had large platforms perhaps intended as defense against flooding. According to a theory first advanced by Wheeler, the city could have been flooded and silted over, perhaps six times, and later rebuilt in the same location. Some archaeologists believed that the site was abandoned after a final flood engulfed the city in a sea of mud. Gregory Possehl was the first to theorize that the floods were caused by overuse and expansion upon the land, and that the mud flood was not the reason the site was abandoned. Instead of a mud flood wiping part of the city out in one fell swoop, Possehl coined the possibility of constant mini-floods throughout the year, paired with the land being worn out by crops, pastures, and resources for bricks and pottery spelled the downfall of the site.