As part of a recent special series on the practice of solitary confinement in prisons, The Guardian interviewed several former inmates who had lived through the experience. One of them, Tyrell Muhammed, had spent seven years in isolation. Muhammed said that after a while ‘you see like the paint on the wall. So you start seeing figurines. In the chips, the paint chips…’ While this recalls Charlotte Gilman Perkins’s account of a descent into madness in ‘The Yellow Wall-Paper’ (1891), it also suggests more broadly the way in which isolation leads some prisoners to seek, and find, designs and patterns where none exist. After years of imprisonment in Vincennes, the Marquis de Sade succumbed to an arithmetical form of this madness which saw him create what he called a ‘number system’: this would lead him to find clues as to the date of his release in the various letters, gifts and visits he received. To give just one example from 1784, ‘When the notary comes, I’ll have been here for 7 weeks and 3 days, with 7 months and 3 weeks left, but nothing from 16 to 9 [. . .] That’s 169 and forms 37. Now all the 37s have ended by making 169. That’s sublime.’ The same obsessiveness with numbers and dates, and the same leaps from reason to unreason, are evident in The 120 Days of Sodom. Numbers matter in the 120 Days, from the ages of the girls and boys in the harems, to the penile dimensions of the ‘fuckers’, to the hours set aside for meals, orgies, and storytelling in the castle of Silling.

Translation itself is something of an obsessive activity. Working on a text like the 120 Days, the devil is in the detail – and that detail soon assumes an importance that may seem out of all proportion to other readers. Sade’s numbers are a case in point. One of the striking features of the text is the way that Sade switches apparently randomly between figures and words to express numbers: ‘the 3 kitchen maids shall serve these two tables, the first of which shall include the 8 little girls and the four old women, the second the four wives, the 8 little boys and the 4 storytellers.’ This switching also extends to the ways in which Sade writes his months: while he sometimes writes them out in full, he often abbreviates them too: thus October becomes 8^ber, November 9^ber and December X^ber – a common practice in the eighteenth century but one which has died out since. While looking for a pattern in such switches can soon resemble a form of madness, we decided it would be wrong to erase them – as all the French editions over the last seventy years have done. What it reveals about the state of mind of the prisoner writing in his cell will be for the reader to decide, but to erase these little differences or eccentricities is to make the text more polished, and more finished, than it really is. This is an incomplete text, part draft and part notes, and we wanted to capture its rough and unready nature.

The circumstances in which Sade wrote his novel were evidently very different from those in which we translated it. Whereas Sade worked alone in his cell, we worked – often together – in the comfort of our own homes or offices; whereas he wrote his draft in thirty-seven consecutive evenings, we took about three years to complete our translation; whereas he wrote in a minute script, barely looking back at what he had already written, we typed away on our laptops, revising draft after draft until we felt the job was done. If we took a lot longer than Sade, it was clearly because we did not work with the same intensity that drove him on night after night. Although our other commitments – personal and professional – may have slowed us down, they also kept us sane, offering the kind of welcome distractions forbidden to Sade throughout his imprisonment in Vincennes and the Bastille. As overwhelming as the process of translation threatened to become at times, particularly when working on the scatological passions of Part One, or the increasingly frenzied violence of Parts 3 and 4, we always had an escape – something that can be said neither of Sade in the Bastille, nor of the doomed prisoners trapped in Silling.