The Alexandria Quartet, Lawrence Durrell's celebrated tetralogy from the 1950s, was defined by its author as "an investigation of modern love", but has often been regarded by its readers more as an evocation of a city – the Greco-Arab, multi-ethnic Alexandria of its title. Almost infinite variations of love are certainly explored in its 1,000-odd pages, and the presence of Alexandria certainly permeates the work, but I think the legendary fascination of the quartet is essentially existential. The work itself is greater than its themes, and casts a spell that is neither precisely emotional nor specifically topographic.

It is actually neither specific nor precise about anything. It was an experimental novel of its day, perhaps related to the work of Durrell's friend Henry Miller, perhaps to Ulysses. It was based on the premise that people and events seem different when considered from different angles and periods, and that they can best be recorded, as Durrell himself put it, stereoscopically. The four volumes concern the same characters, but each of the several narrators tell the novels' complex tales from their own viewpoint, and they write at different times. It is a device, Durrell claimed, amounting to a new concept of reality, reflecting the ideas of Freud and Einstein and a convergence of western and eastern metaphysics.

If that sounds over-blown, well, the Quartet itself is not without pretension, in concept as in performance. As has generally been admitted, it is often ornate and over-written, sometimes to an almost comical degree. The high ambition of its schema can make its narratives and characters inexplicably confusing, and its virtuoso use of vocabulary can be trying ("pudicity"? "noetic"? "fatidic"? "scry"?). But if there are parts of the work that few readers, I suspect, will navigate without skipping, there are many passages of such grand inspiration that reaching them feels like emerging from choppy seas into marvellously clear blue Mediterranean waters.

For it is true that the city of Alexandria does colour the entire work. Durrell lived and worked in the city from 1942 to 1945, and he believed strongly in the effect of place on human temperament. Alexandria's peculiar Levantine character, as it existed during Durrell's time there, is insistently summoned into these pages. His responses to the place were moulded partly by EM Forster's elegant Alexandria, A History and Guide, first published in 1922, and more especially by the greatest of Alexandrine poets, Constantin Cavafy – who had died in 1933, but whose drifting presence in the books is almost as haunting as the presence of the city itself.

It was Cavafy who wrote of Alexandria "There's no new land, my friend, no / New sea; for the city will follow you, / In the same streets you'll wander endlessly …" One of this work's narrators goes further still: "Man is only an extension of the spirit of place," says Nessim (I think it is) in Justine. The several narrators of the Quartet are certainly enslaved by Alexandria's genii loci, and readers are likely to be entrapped too, because the work, so opaque is other contexts, is clear enough when it deals with the city. We soon learn the geography of the place, from the handsome Rue Fuad to the meshed Arab backstreets, from the elegance of L'Etoile or the Cecil Hotel to the hashish cafés of the slums or the sandy approaches to the Western Desert. We see inside the mansions of rich cosmopolitans and diplomats, we visit stifling attic bedrooms, brothels and pleasure pavilions by the sea.

Much of all this is factual. Durrell based much of his fiction on personal experience, reminiscence and tittle-tattle, which gave the Quartet, for his contemporaries, something of the allure of a roman-à-clef, not least in its sexual allusions. In fact a general sensuality is the most Alexandrine aspect of the Quartet, but it does shows itself, too, in somewhat hazy illustrations of individual sex – "modern love", as Durrell put it. These "dark blue tides of Eros" are far from pornographic. Sometimes, it is true, we are unsure who is loving whom, and now and then there are homosexual and cross-dressing deviations, but mostly the love elements are straightforward and moving, and really do dominate, as Durrell implied, the devious goings-on of the plot.

Which is full of surprises. Some, I dare say, really are Freudian or Einsteinian in origin, or metaphysically intercultural, but they seem to me more like twists in a skilful thriller, closer to Le Carré than to James Joyce, and sometimes embroiled in melodrama – "the slime of plot and counterplot", as another of Durrell's characters defines it. He was particularly admired for his descriptive writing, and these books are rich in masterly set-pieces, but he was also a fine storyteller, adept in techniques of suspense and deception. Reader, watch out! Shocks are always around the dusty corner.

The four books of the tetralogy originally appeared separately – Justine in 1957, Balthazar and Mountolive in 1958, Clea in 1960. They were immediately recognised as remarkable works of art, but the verdict on the whole work, while always respectful, was mixed. French critics adored it. Americans lapped it up. English reviewers were not so sure. Durrell, a lifelong expatriate, never was an admirer of English culture, and his elaborate prose did not greatly appeal to more austere littérateurs such as Angus Wilson, who called it floridly vulgar. Its pretensions were mocked, its avant-garde excesses parodied, and although the books were commercial triumphs, he wrote nothing so publicly successful again.

But the whole thing itself, this immense imaginary construction, has stood the tests of time and taste, and has never been out of print – probably never will be. Half a century after its completion, those florid vulgarities, those modernist pretensions, seem no more than incidental to its unique flavour, which lingers in the mind long after its labyrinthine plots (for they are myriad, and muddling) have been forgotten.