How did 4,500-year-old Indus cities get drains, wells and standard weights?

About 4,500 years ago, in what is now Pakistan and north-west India, people built cities that planned for water. They belonged to the Indus Valley Civilisation, a Bronze Age civilisation that lasted from 3300 BCE to 1300 BCE, and in its mature form from 2600 BCE to 1900 BCE. It was one of four centres of the ancient world, with Egypt, Mesopotamia and China, and it was geographically larger than Egypt and Mesopotamia combined.

Its cities were noted for urban planning, baked brick houses and elaborate drainage systems. At Mohenjo-daro the buildings stood on a grid, waste water ran into covered drains that lined the major streets, and archaeologists have found more than 700 wells, a number unheard of among other civilisations of the time. Mohenjo-daro and Harappa very likely held between 30,000 and 60,000 people each.

The Harappans also measured carefully. They were among the first to develop a system of uniform weights and measures, and an ivory scale found at Lothal has a smallest division of about 1.704 mm.

What is missing is as striking as what is there. Unlike Mesopotamia and Egypt, the Indus civilisation built no large monumental structures, and there is no conclusive evidence of palaces or temples. Some houses were larger than others, yet all had access to water and drainage, which gives the impression of a society where wealth was not heavily concentrated. Who ruled these cities and how? Archaeological records provide no immediate answers.