The mature Indus civilization flourished from about 4600 to 3900 years ago. It included urban centers such as Dholavira, Kalibanga, Ropar, Rakhigarhi, and Lothal in modern-day India, and Harappa, Ganeriwala, and Mohenjo-daro in modern-day Pakistan. The cities were built of brick, with roadside drainage system and multi-storied houses. During the later period of this civilisation, signs of a gradual decline began to emerge. By about 3700 years ago, most of the cities were abandoned. However, the Indus Valley Civilisation did not disappear suddenly. Some parts of the Indus Civilization may have survived in the smaller villages and isolated farms.