The Sarasvati River was the largest in ancient India, flowing west of Delhi and providing water to a fertile region as described in the Rig Veda, which is the most fundamental of the sacred Vedic Hindu texts. (The river has since completely dried up, but was proven to have existed by looking at satellite photographs of India.) Food and commerce along the river was based on barley, (yava), copper (ayas) and cattle. By 2600 B.C., the Indus-Sarasvati civilization became the largest civilization in the ancient world, spreading from Pakistan to many areas of India today. It had links to Mesopotamia, Afghanistan, Central Asia and elsewhere. Its population is estimated to have been 100,000.