The Marquis de Sade is one of those few writers who have given the world an adjective. The problem is that this has become a kind of shorthand: without reading Sade everybody presumes to know what he is all about. It is only when you pay close attention to his work that you begin to understand that his writing is not erotica, not even really pornography, but something else much more monstrous, grotesque and nightmarish.

His masterpiece was “The 120 Days of Sodom”, which has just been published as a Penguin Classic for the first time. It is a compendium of murder, torture and sexual crimes which tests the limits of the human imagination. This is not an easy book to read; its viciousness is occasionally breathtaking. But what really threatens to break the reader’s nerve is the overwhelming atmosphere of claustrophobia. Sade is in this sense Kafkasque – not just the Kafka of “The Trial” or “The Castle” but also of “The Penal Colony”, a world ruled by cruelty and evil, where all hope of redemption or release is impossible.

This much is hardly surprising, since the book was composed in a prison cell. By the time of the French Revolution in 1789, Sade had been in jail for 11 years, first in Vincennes and then the Bastille. He was originally arrested on charges of poisoning and sodomy, and wasn’t cleared until 1790. Held without trial, he spent his time gorging himself, masturbating and writing the scroll of “The 120 Days of Sodom”. He worked on it each evening, for safety’s sake transcribing it in tiny handwriting onto sheets of paper, which could then be hidden in the crevices of the prison wall.

The four main characters in the book are a duke, a bishop, a magistrate and a financier, representing the groups who held together the moral and political order in France (and were therefore responsible for keeping Sade in prison). They have all grown rich and powerful during the reign of Louis XIV, but are now jaded and desperate to re-ignite sexual excitement. To this end, they organise a month-long orgy in a medieval castle deep in a forest (probably the Black Forest). The story is then structured around a series of debauches described in a mainly dispassionate voice, although the narrator occasionally breaks through to let the reader know that he is telling this tale in order to teach them to hate vice. It was this skewed, deliberately disingenuous perspective that led Simone de Beauvoir to describe Sade as a moraliste, who encourages people to be good by revolting them with evil.

And revolting it is. For much of the text it is as if Sade is trying to insult or humiliate the reader by leading him or her into the far reaches of depravity, and in the very act of reading about it, making them complicit in it. This, at least, was the view of the novelist and philosopher Georges Bataille, no stranger himself to writing about sexual extremes. Sade – the bored and morbidly obsessed prisoner – takes his revenge on the world by creating literature which is not only about evil, but, in its power to subvert, disturb or corrupt, is evil.

“The 120 Days of Sodom” is a historical document that matches and illustrates the tensions of pre-revolutionary France, a country in historical free-fall. In their scholarly and wise introduction, the translators of Penguin’s new edition, Will McMorran and Thomas Wynn, are careful to emphasise the historical context, pointing out that for large chunks of his posthumous career Sade was more discussed than read (they give many good examples, including Myra Hindley and Ian Brady, who read bowdlerised versions of Sade). They also provide a guide to how the book has entered contemporary French thought. As well as Bataille, Sade’s other influential readers include Pierre Klossowski, who focused on the rationalism of his atheistic system, and Annie LeBrun, who defined Sade as the prophet of the post-Enlightenment era. Above all, however, the great merit of this edition is the thoroughly excellent translation by McMorran and Wynn. It has none of the phoney archaism of earlier English translations. Instead it is like a window, allowing us to have as clear of view as possible of Sade’s mind and world.

The quality of Sade’s mind is the reason that he is still worth reading in the 21st century – if you have the stomach. In his own time, his appalling vision of Absolute Freedom was an accurate mirror of the real atrocities of the Terror. Later Raymond Queneau, a French novelist, wrote that Sade’s writings were “a hallucinatory precursor of the world ruled by the Gestapo, its tortures, its camps.” Albert Camus agreed, noting that “from Sade’s lurid castle to the concentration camps, man’s greatest liberty consisted only of building the prison of his crimes”.

But the gravest insight that Sade’s writing contains is that the impulse to inflict pain on other human beings is simultaneously about sex and power. To this extent, the sadistic act is about politics as much as it is about sexual appetite. It is this aspect of his thinking that has fixed Sade’s image then as now as the master theorist of transgression, the bloated figure in Man Ray’s famous surrealist portrait who gazes with a piercing eye into the blank and infinite space of the future. With the abuse at Abu Ghraib a recent memory, and with ISIS atrocities still ongoing, Sade’s novel feels as grimly relevant to the terrors of our age as to those of his own.