Write in short the story of discovery of the Harappan Civilisation.

By 1800 BCE we find that most of the Harappan site abandoned and people shifting towards new settlements in Gujarat, Haryana, Western UP etc and people began to forget about its existence. It was in 1842 where it was first described by charles Masson in his book Narrative of Various Journeys in Balochistan, Afghanistan, and the Punjab. 

However it was ASI director general Alexander Cunnigham who started excavating the site but he made the mistake of placing the dug object between 6th century BCE to 4th century BCE because he like many others, thought that Indian history began with the first cities in the Ganga valley. But the significance of the objects found from the sites came into limelight only in the early twentieth century when Daya Sahni, Rakhal Das Bannerjee began to find objects in the layer of soil which were much older than 6th century BCE. 
Later on with John Marshall as the director General of the ASI the view changed, he was the one who declared the find of new civilization. Though he was a trained archaeologist he ignored while digging the stratigraphy of the soil, hence many important context of the finds were lost. It was only with R E M Wheeler who became the Director General of the ASI in 1944 that rectified this problem. Wheeler recognised that it was necessary to follow the stratigraphy.
Later new archaeologist discovered new sites. And we began to have new understanding of civilization which was not discovered till late in the 19th century.

Tips: -

V. Imp.