Excerpts from Books and Wikipedia
The Black Hole was a small building or cell in Fort William in Calcutta. The British continued to defend Fort William despite the orders of the Nawab (ruler) of Bengal. One hundred forty-six people were crammed into the cell overnight, and the British claimed that 123 people died from heat illness. Robert Clive and the British East India Company used the atrocity to justify the conquest of Bengal. Later, Holwell (who had been imprisoned in the Black Hole) became governor of Bengal." [Furtado: 1001 Days]