Indus River, Tibetan and Sanskrit Sindhu, Sindhi Sindhu, or Mehran, great trans-Himalayan river of South Asia. It is one of the longest rivers in the world, with a length of some 2,000 miles (3,200 km). Its total drainage area is about 450,000 square miles (1,165,000 square km), of which 175,000 square miles (453,000 square km) lie in the ranges and foothills of the Himalayas, the Hindu Kush, and the Karakoram Range; the rest is in the semiarid plains of Pakistan. The river’s annual flow is about 58 cubic miles (243 cubic km)—twice that of the Nile River and three times that of the Tigris and Euphrates rivers combined. The river’s conventional name derives from the Tibetan and Sanskrit name Sindhu. The earliest chronicles and hymns of the Aryan peoples of ancient India, the Rigveda, composed about 1500 BCE, mention the river, which is the source of the country’s name.