Instructions: The answer to this question can be given by stating the year in which the excavation started. Information about the bricks is also important.
Solution: In 1921, when Sir John Marshall was the director of the Archaeological Survey of India, an excavation was carried out at a site in Indus Valley from where some old bricks were found.. These bricks, which were taken from an old ruin for the construction of a railway line in 1856 were found to be very old, belonging to ancient ages.The excavations revealed the existence of a great civilization in the valleys of the river Indus and its tributaries. And finally a civilization was discovered which was named as the Indus valley civilization.