One of the largest rivers in the world, the Indus rises in the Tibetan mountains, flows west across northern India and south through Pakistan. For millennia it has been worshipped as a god; for centuries used as a tool of imperial expansion; today it is the cement of Pakistan's fractious union. Five thousand years ago, a string of sophisticated cities grew and traded on its banks. In the ruins of these elaborate metropolises, Sanskrit-speaking nomads explored the river, extolling its virtues in India's most ancient text, the Rig-Veda. During the past two thousand years a series of invaders - Alexander the Great, Afghan Sultans, the British Raj - made conquering the Indus valley their quixotic mission. For the people of the river, meanwhile, the Indus valley became a nodal point on the Silk Road, a centre of Sufi pilgrimage and the birthplace of Sikhism. Empires of the Indus follows the river upstream and back in time, taking the reader on a voyage through two thousand miles of geography and more than five millennia of history redolent with contemporary importance.