Somewhere around the second century CE, near present day Thanjavur, a Chola king named Karikala put thousands of labourers to work sinking unhewn stone into the sandy bed of the Cauvery to make a dam, in a hope that it could supply water to his kingdom. To everyone’s surprise, no mortar was used to hold it together; there were only rocks laid against rock for more than three hundred metres, across a mighty river that flooded every year without fail. I’ve often wondered what h