This is, for 10 points, what June 20th, 1756 incident in which many British prisoners were suffocated after being locked overnight in a small room?
A monument commemorating this was built in Dalhousie Square, although after it attracted political controversy, it was moved to St. John's Church. This event was preceded by the capture of a silkworm factory at Kasimbazar and governor Roger Drake's retreat from Fort William. Roger Clive eventually rescued many of the survivors; one of them, John Holwell, claimed that 123 people died, although later counts showed it was at most 43 people, all of whom had been imprisoned by the forces of Siraj-ad-Daula, the Nawab of Bengal. This is, for 10 points, what June 20th, 1756 incident in which many British prisoners were suffocated after being locked overnight in a small room?
A monument commemorating this was built in Dalhousie Square, although after it attracted political controversy, it was moved to St. John's Church.
{Black Hole} of {Calcutta} [or {Black Hole} of {Kolkata}]