Reference

The "Mature Harappan phase" of the Indus Valley Civilization took place from about 2600 BC until around 1900 BC. Although there was continuity of Indus Valley cultural traditions from the Early to the Mature Harappan phases, many of the unique hallmarks of the civilization were established after 2600 BC.

Mature Harappan Phase. By 2600 BC, Indus Valley Civilization had entered into a mature stage. The early Harappan communities were turning into large urban centers, like Harappa and Mohenjodaro in Pakistan and Lothal in India. The concept of irrigation had also been introduced. The following features of the Mature Phase were more prominent: Cities

The lifespan of the Indus Valley Civilization is often separated into three phases: Early Harappan Phase (3300-2600 BCE), Mature Harappan Phase (2600-1900 BCE) and Late Harappan Phase (1900-1300 BCE). At its peak, the Indus Valley Civilization may had a population of over five million people.