Final answer:
The great bath of the Indus Valley Civilization was made watertight using a layer of bitumen, demonstrating significant ancient engineering skills for both utilitarian and ceremonial purposes.
Step-by-step explanation:
The great bath, often associated with the advanced urban settlement of the Indus Valley Civilization, particularly in the city of Mohenjo-Daro, was engineered to be watertight. This was achieved with a layer of a natural tar-like substance called bitumen, which was used as a sealant. The design and construction techniques were so effective that they allowed these baths to hold water without leaking, a remarkable feat of ancient engineering. The baths were not only for hygiene but also held a significant cultural and ritualistic role. The precision and care in their construction are indicative of their importance in the society of the time.