The ancient city of Harappa lies around 150 miles north of Lahore in Pakistan. It was once one of the great centres of a civilisation that has largely disappeared, one with vast trade connections and boasting several of the world's first cities. At a time when another great civilisation was being forged along the banks of the river Nile in Egypt, Neil MacGregor investigates this much less well-known civilisation on the banks of the Indus Valley. He introduces us to a series of little stone seals that are four-and-a-half thousand years old, covered in carved images of animals and probably used in trade. The civilisation built over 100 cities, some with sophisticated sanitation systems, big scale architecture and even designed around a modern grid layout. The great modern architect Sir Richard Rogers considers the urban planning of the Indus Valley, while the historian Nayanjot Lahiri looks at how this lost civilisation is remembered - by both modern India and Pakistan.