The valley of the Indus and its tributaries is divided today between India and Pakistan. Some 7,000 years ago the valley was one of the cradles of civilization. From the Indus Valley, Dravidian people spread agriculture and fixed settlements across India, arriving in the far south about 4,000 years ago. The Indus Valley Harappan civilization, a Bronze Age culture, flourished from around 2300 to 1500 BC and had links with western Asian civilizations in Iran. The two great cities of the Harappan civilization—Mohenjo-Daro and Harappa—are in what is now Pakistan, but Harappan culture also thrived in northwestern India. Writing, fine jewellery and textile production, town planning, metalworking and pottery were the hallmarks of an advanced urban society, which collapsed for reasons unknown.