Labour was carried out by paid workers as well as by contingents of slaves, particularly Christian prisoners.[1] Estimates on the total number of workers involved range from 25,000 and 55,000.[2][8] Nonetheless, frequently-told stories about the tens of thousands of Christian slaves used for labour and the large underground dungeons where they were kept are somewhat exaggerated and originate from the accounts of European ambassadors who visited Isma'il's court (often to negotiate the release of prisoners from their countries).[4] In reality, the number of Christian slaves was likely closer to a few thousand at most and the chambers popularly called "prisons" were actually storage rooms for grain and supplies.[4]:106[4]:267 Marianne Barrucand, in her study of Moulay Isma'il's construction projects, cites earlier research that estimates the number of Christian slaves in the first half of Isma'il's reign between 550 and 650, and at around 800 in 1708.[5]:122