The Mature Harappan phase of the Indus Valley Civilization began around 2600 BC. During this phase, the cities of Harappa, Lothal, Kalibangan, Dholavira, Rakhigarhi and Mohenjo-daro grew into large metropolises as the civilization expanded to over 2,500 cities and settlements. The Indus script also matured and began being used by the civilization.