[3] Although popularly described as an underground prison that could host thousands of inmates, mostly Europeans captured at sea,[4] most scholars agree that its function was to serve as a vast storage space for the royal complex of the Kasbah of Moulay Ismail.

[3] Another account says that the location was only named thus during the French occupation and that the appellation derives from the nickname of the prison guard who was reportedly bald (Moroccan Arabic: قرع qrəɛ).

Moulay Ismail chose Meknes, a city that held no special significance intellectually or politically prior to his reign, for strategic reasons, and possibly to leave his own fingerprint as monarch, outside of the shadow of preceding Moroccan dynasties.

[5] Prisoners and slaves were used in the construction of the underground vault and the wider complex,[1] although scholarly studies have estimated that they were only a small part of the total workforce.

[1] According to Moroccan historian Ibn Zaydan, its structure was strong and resilient since "riders passed on top of it, beasts of burden dragged big rocks, and loaded vapor vehicles drove night and day above it, and even gardens with big trees were planted and often irrigated, with no effect on its build".