The important site of Harappa, part of the Indus Valley Civilization, was first extensively excavated by Rai Bahadur Daya Ram Sahni in 1921. This excavation led to the discovery of the civilization. R.D. Banerjee discovered Mohenjo-daro in 1922. Sir John Marshall was the Director-General of the Archaeological Survey of India at the time and announced the discovery of the Indus Valley Civilization to the world in 1924, based on the findings at Harappa and Mohenjo-daro. R.S. Sharma is a historian who wrote extensively on ancient India, not the primary excavator of Harappa.