Along with Mesopotamia and Egypt, the Indus Valley Civilization ca 4000-1500BC is amongst the three oldest in the world
Although thought to have been confined to the valley of the river Indus- hence the name, it was a highly developed urban civilization and spread across nearly 500,000 square miles
The major cities Harappa(3300BC) and Mohenjo-Daro(2500BC) -were well planned, houses built with baked bricks- and had an elaborate system of developed sewage/water systems -centred in what is now western India and Pakistan.
Trade seemed to be a major activity - decimal fractions and uniform weights/measurements were used.The seals found are in various shapes and size. The elegant script though is still being deciphered by scholars