What happened during the imprisonment known as the Black Hole of Calcutta?

The incident known as the Black Hole of Calcutta occurred on June 20, 1756, following the capture of Kolkata by the nawab of Bengal, Sirāj al-Dawlah.

After the East India Company’s garrison surrendered, the remaining European defenders were confined overnight in a small local lockup for petty offenders, measuring 18 feet by 14 feet with only two small windows.12

Historical accounts of the event vary significantly. John Z. Holwell, a survivor, claimed 146 people were imprisoned and only 23 survived. Later analysis, including a 1959 study, suggests the number of captives was closer to 64, with 21 survivors. While the incident was long used to characterize the nawab as callous and to justify British imperialism, modern historians note that the nawab’s role was likely one of negligence rather than intentional cruelty, and the details of the event remain a subject of historical controversy.12