The "Black Hole of Calcutta" was a tiny prison cell in Fort William, in the Indian city of Calcutta.
According to John Zephaniah Holwell of the British East India Company, on June 20, 1756, the Nawab of Bengal imprisoned 146 British captives inside the airless room overnight. When the chamber was opened the next morning, only 23 men (including Holwell) were still alive.
This story inflamed public opinion in Great Britain, and led to the characterization of the Nawab, Siraj-ud-daulah, (and by extension all Indians) as cruel savages.
In fact, no other contemporary sources ever corroborated Holwell's story, and he was caught fabricating other incidents.
Furthermore, given the dimensions of the room (24 feet x 18 feet), it would not have been possible to cram more than about 65 prisoners into the space.
Holwell's account may have been mere exaggeration. Then again, it may be that the incident was entirely a figment of his imagination.
The story of the "Black Hole of Calcutta" actually could be one of history's great scams, along with the "bombing" of the battleship Maine in Havana Harbor, the Gulf of Tonkin Incident, and Saddam Hussein's putative weapons of mass destruction.
Whatever the truth of the case, the young Nawab was killed the next year at the Battle of Plassey, and the British East India Company assumed control over most of the Indian subcontinent.