Mohenjo-daro's Great Bath
2500–1900 BCE
The Great Bath of Mohenjo-daro, built around 2500 BCE, is the world's earliest known public water tank. Its construction reveals a level of hydraulic engineering sophistication that would not be matched in the Western world for 2,000 years. The bath was waterproofed with bitumen, fed by a dedicated well, and drained by a corbelled drain — all in a city that also had the world's first known urban sewage system.
The Indus Valley Script
2600–1900 BCE
The Indus Valley Civilisation — the largest of the ancient world's four great civilisations, covering an area larger than Egypt and Mesopotamia combined — left behind over 4,000 inscribed objects bearing an undeciphered script. Despite over a century of attempts by linguists and cryptographers worldwide, the Indus script has never been decoded. We know nothing of the language, religion, or history of a civilisation that housed over 5 million people.