The Indus city of Mohenjo-daro had plumbing 4,500 years ago and a script still undeciphered

Around 2500 BC, in what is now the Sindh province of Pakistan, a city of tens of thousands of people was laid out on a grid, supplied with covered drains and equipped with private bathing rooms in ordinary homes. Mohenjo-daro was one of the largest centers of the Indus Valley civilization, and its sanitation infrastructure was more advanced than that of many cities built thousands of years later. Yet the people who engineered it left behind a script that has never been read.

The combination is striking. A society capable of planning an entire urban water and waste system on this scale plainly kept records and communicated in writing, but those writings survive only as brief inscriptions no scholar has managed to decode. Much of what the city meant to its inhabitants is therefore reconstructed from bricks and drains rather than from their own words.

A city planned on a grid

Mohenjo-daro covered a large area, with estimates of its extent running to several hundred acres, and was divided into a raised citadel and a lower residential town. Streets ran in an orderly grid oriented roughly to the cardinal directions, with major thoroughfares dividing the city into large blocks, and buildings were constructed from standardized fired bricks of consistent proportions, evidence of centralized planning and shared standards. Estimates of the population run to the tens of thousands at its height. As the UNESCO World Heritage listing notes, the site is among the most important surviving examples of the Indus civilization’s urban design, built and rebuilt over centuries on the Indus floodplain.

The uniformity extended beyond architecture. The Indus civilization used a standardized system of weights based on regular ratios, along with consistent brick dimensions across cities separated by hundreds of miles, pointing to shared administration or strong cultural norms. Notably, excavators found no obvious palaces or monumental royal tombs of the kind that dominate contemporary Egypt or Mesopotamia, which has led some scholars to suggest a society organized differently from the god-king states of the same era, though the absence of readable records leaves the political structure uncertain.

Plumbing ahead of its time

The feature that most impresses modern engineers is the water and waste system. Many houses had their own wells, bathing platforms and latrines, and wastewater was channeled through a network of covered brick drains running beneath the streets. This meant that a large share of the population had access to private sanitation, an arrangement that would not become common in cities elsewhere until comparatively recent history. The drains included features to manage flow and inspection, reflecting deliberate design rather than improvised construction.

The Great Bath

The most famous structure at the site is the Great Bath, a rectangular tank set within the citadel and generally regarded as the world’s oldest known public water tank. According to Britannica, the basin was built from tightly fitted fired bricks sealed with a layer of bitumen to make it watertight, with steps leading down into the water at each end. Its likely purpose was ritual bathing, suggesting that cleanliness carried religious or ceremonial meaning in Indus society. The care taken to waterproof and drain the tank shows the same engineering sophistication seen in the city’s domestic plumbing.

A script that resists reading

The Indus civilization produced thousands of inscribed objects, most of them small seals bearing a few signs alongside images of animals. More than 400 distinct signs have been catalogued, but the inscriptions are extremely short, typically only a handful of characters, and no lengthy texts or bilingual keys have been found. Without a longer body of writing or a translation into a known language, scholars have been unable to determine even whether the script records a full spoken language or a more limited system of symbols. The result is that the Indus script remains undeciphered, and the names, laws and beliefs of Mohenjo-daro’s people stay out of reach.

An unexplained decline

By around 1900 BC, Mohenjo-daro and other major Indus cities were in decline, and the reasons are debated. Proposed factors include shifts in the courses of rivers, changes in climate and monsoon patterns that undercut agriculture, and disruptions to trade. Because the writing cannot be read, there is no internal account of what happened, and the collapse must be pieced together from environmental and archaeological evidence. The city was rediscovered in the 1920s during surveys by the Archaeological Survey of India, which revealed that the Indus civilization had been a peer of ancient Egypt and Mesopotamia rather than a minor culture. Among the finds were small masterpieces of Indus art, including a carved stone bust often called the Priest-King and a bronze figurine known as the Dancing Girl, objects that showcase the craftsmanship of a people whose language remains silent. Now inscribed as a UNESCO World Heritage Site, Mohenjo-daro faces modern threats from erosion, salt damage and weathering, adding urgency to preserving a city that engineered running water and waste removal 4,500 years ago yet still cannot tell its own story.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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