Indus civilization, also called Indus valley civilization or Harappan civilization is the earliest known urban culture of the Indian subcontinent. The nuclear dates of the civilization appear to be about 2500-1700 BCE, though the southern sites may have lasted later into the 2nd millennium BCE. The Indus civilization is known to have consisted of two large cities, Harappa and Mohenjo-daro, and more than 100 towns and villages, often of relatively small size. The two cities were each perhaps originally about 1 mile (1.6 km) square in overall dimensions, and their outstanding magnitude suggests political centralization, either in two large states or in a single great empire with alternative capitals, a practice having analogies in Indian history.