One morning early in 1857, Mark Thornhill, a British magistrate in the Indian town of Mathura, came into his office to find four small chapattis lying on his desk. These “dirty little cakes of the coarsest flower” had been sent to him by a puzzled village watchman, who had been handed them by a stranger and confessed that he had no idea what they were.

There was nothing unusual about the chapattis themselves; they were identical to the breads cooked in every home in India. Yet Thornhill’s enquiries elicited the discomforting information that thousands of the things were passing from hand to hand throughout his district.