Chronology of Indus Valley civilizations not yet been fixed beyond doubt. This is primarily because first the calibration of the radio-carbon dates had to be corrected on the basis of researches coming out from the radio carbon laboratories; secondly scholars seem to be not really in agreement about where they should begin to count the emergence of the Indus culture.
This will be amply demonstrated by the fact that what was earlier termed as Pre-Harappan has now been included as Early Harappan. Likewise, Mature Harappan is renamed as urban phase of Harappan. And what was considered as Late Harappan is now renamed as Post Urban phase of Harappan.
Initially, Sir John Marshall estimated the Indus Valley civilizations as having emerged around 3100-2750 B. C. Mortimer wheeler subsequently re-examined the archaeological evidences specially the scale of Mesopotamian culture and established a contact of sorts with the Indus.
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On the basis of the latter and the similarities Wheeler felt that the civilization ranged between 2500 to 1500 BC. D. P. Agrawal also tried to re-establish the date and announced that Indus ranged between 2350 to 1700 BC.
In the recent years many more C14 dates form a larger number of sites have become available. These indicate that Early Harappans decidedly occur earlier than 2500 BC and may even be as old as 3000 BC. The date for mature harappans or Urban Harappans is estimated to be 2500 BC to 2000 BC.
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Late harappan or Post Urban Harappan in the same light is pushed to 2000-1500 BC and it is believed that at some sites it might even extend to 1200 BC. The interlocking of P. G. W. which is an iron using culture at Mitathal or Ganga-Jamuna sites should surely be taken as the Late Harappans continuing to survive till very young period.