Steatite seal and Bricks of a standardised ratio are the most distinctive artefacts of the Harappan Civilisation. Steatite is a talc-schist, which is a type of metamorphic rock; it is very soft and has been a medium for carving for thousands of years. Harappans are known for seal carving which is the cutting of patterns into the bottom face of a seal, a small, carved object used for stamping. The smaller bricks were used for the construction of residences and other smaller houses while the larger ones were used for public buildings, walls, etc. Both the types of bricks followed a ratio of 1:2:4. The Indus Valley Civilisation is the earliest known culture of the Indian subcontinent and the largest of the four ancient civilisations, which also included Egypt, Mesopotamia and China.