The Elgin Marbles are the world's most contested cultural artefacts. Soon after the sculptures were put on display at the British Museum in 1816, the Greeks demanded their return. These claims have reached a crescendo in recent years, thanks in part to the missionary zeal of Melina Mercouri, the Greek minister for culture in the 1980s, but also due to increasing worldwide pressure for the repatriation of cultural treasures acquired in controversial circumstances.
One of the main arguments - and one of the few aesthetic ones - put forward by those who want the Elgin Marbles returned is that they have a negligible impact on British art. This is an important point, because it has always been claimed that the sculptures are more influential by virtue of being situated in the British Museum - with its "ideal" viewing conditions and central location in a "world city" - than they would be in the less populous and less visited city of Athens.
Increased access to artworks has always been central to the ideology of national museums, and has been an alibi for the removal of all kinds of fixtures and fittings from "inaccessible" churches and temples. Lord Elgin himself was in no doubt about the educational potential of the Parthenon sculptures. He hoped to bestow "some benefit on the progress of taste in England", and to improve not just the fine arts, but even the design of household goods.
If it can be proved that, in terms of influence, the Elgin Marbles are tantamount to a white elephant, then the case for keeping them in London would seem to be weakened. That is the line taken by Christopher Hitchens in his polemical tract, The Elgin Marbles: should they be returned to Greece?, which was first published in 1987, and re- published by Verso last year, to great media excitement. Hitchens says that, although the Parthenon frieze has become "familiar in English architecture and design in a manner that must belong to Elgin", even the "staunchest John Bull would not claim this as an especially rich harvest". He is referring primarily to pastiches of the frieze that adorned buildings such as the Athenaeum Club and the Hyde Park arch, and that were used to decorate china.
Stephen Bayley ran with this idea in a feature in the Independent last June headlined "Good riddance: who needs the Elgin Marbles?". Bayley claimed they arrived here "when classicism was a spent force", and that they are irrelevant to the kind of artist shown in Tate Modern: "Tracey Emin and Cornelia Parker . . . possess astonishing talent that operates in the modern world, not in the antiquity of the Horse of Selene and the Battle of Lapiths and Centaurs."
Yet both Hitchens and Bayley are misguided: the Elgin Marbles stimulated the production of high-quality art in the 19th century, and they continue to do so in the 21st. Bayley's belief that they are irrelevant to today's artists could scarcely have been worse timed. The shockwaves of the Elgin Marbles are still reverberating through the British art world - and through Tate Modern.
Early viewers had no doubt about their importance. They had been brought up to venerate sculptures such as the Apollo Belvedere and the Medici Venus, which were highly restored Roman copies of Greek originals. But these seemed slick and effete in comparison to the naturalism of the unrestored Greek sculptures designed, if not executed, by Phidias himself. The sculptor John Flaxman said that, in comparison to the pedimental figure then known as the Theseus, the Apollo Belvedere was a dancing master.
From 1807-11, the marbles were exhibited in a damp, ramshackle shed next to Lord Elgin's house in Park Lane. The raw vigour of the sculptures was intensified by their being left unrestored as fragments, and exhibited in picturesque disarray, close to hand. Lord Byron was horrified and called them "Phidian freaks". The display was even more down-to-earth when they were exhibited in the British Museum. Never before had a major museum installed its principal masterpieces in such a utilitarian way. The galleries were designed to enable artists and students to draw and sketch the sculptures from every angle with the best natural light. To this end, some of the pieces were mounted on swivel pedestals so that they could be easily rotated. The French connoisseur Quatremere de Quincy was hugely impressed: "Here," he wrote, "you are on the building-site or in the studio itself, and the objects are to hand in their actual dimensions; you can move around each one, counting up the fragments, assessing relationships and measurements."
At this point, art historians usually say that, despite the widespread excitement at the naturalism of the Elgin Marbles, the most important manifestation of naturalism in British art was in Romantic landscape painting, which could scarcely be influenced by them. But this is disproved by the example of John Constable. Even though Constable never mentions them in his letters, I believe that the Elgin Marbles, and the way in which they were installed, were a major catalyst for his later work. The simple, "horizontal" way in which the marbles were displayed made them easier for a landscape painter to assimilate. Their presence in London helps to explain the more heroic scale and feel of Constable's late figures, the greater prevalence of fragmented and weathered forms, and the flickering impasto.
A motif that is first found in Flatford Mill (1817), and which is repeated in paintings such as View on the Stour near Dedham (1822) and The Lock (1824), is that of a man on a barge, leaning and pushing at an acute angle on a pole or pulling a rope. The mise-en-scene involving these men and their barges is comparable to that of the reclining pedimental figures and their mobile pedestals. The Leaping Horse (1825) has been compared to Italian Renaissance equestrian monuments, but the way in which the horse's legs seem to be entangled with the angular wooden barrier is reminiscent of the Parthenon metopes where centaurs leap awkwardly on to their enemies, the lapiths.
William Hazlitt, a contemporary of Constable, saw the marbles as a manifestation of nature in action: "There is an undulation and a liquid flow to the surface, as the breadth of genius moved the mighty mass." The deep undercutting and swirling rhythms of the robes of the pedimental figures contributed to the sense of elemental ebb and flow; so, too, did the quasi-chronophotographic repetition of the horses on the frieze. Constable seems to have been after a comparable effect with his thick, busy impastos. The willow stump in the centre of The Leaping Horse has a vibrant shimmer that recalls the draped fragment figures of Iris and Hebe.
The surface effects pioneered by Constable, and hinted at in the Elgin Marbles, were followed up in France, rather than Britain. In the late 19th century, however, George Frederick Watts deployed complex surface effects in sculpture as well as painting. Watts claimed that his "only teachers were the Elgin Marbles". His most celebrated sculpture, Physical Energy (1883-1906, Kensington Gardens), shows a naked man on a rearing horse. The horse's head is closely based on that of the horse of Selene, and the form of the rider is broadly that of Dionysus. Watts saw his statue as a symbol of the energy and progress that typified the "age of empire". The first casting of 1902-03 was set up as a memorial to the arch- imperialist Cecil Rhodes in Cape Town.
Yet there is a strange sense of impending collapse. The profile of the sculpture is blockish and crumpled, and the surface is extremely rough and pitted, like a piece of weathered pumice stone. The rider leans sharply back and shields his eyes with his hand, as though dazzled by the sun. The maquette, on which the elderly artist laboured for years, had detachable arms and legs, and Watts often thought it looked better fragmented than complete. What he seems to have taken from the Elgin Marbles is their pathos. When the poet John Keats saw them for the first time, their damaged state reminded him of his own mortality, and made him wonder if he would die "like a sick eagle looking at the sky". This sickness, this failure to fly, is the real subject of Physical Energy. The Elgin Marbles made viewers think about the fragility, as well as the power, of empires.
In the 20th century, despite increasing appreciation of primitive and non-western sculpture, the Elgin Marbles have become even more significant. The reclining figure has an almost mythical status in modern British art, thanks to Henry Moore, and the development of a taste for sculpture with a horizontal orientation. The principal source for the motif of the reclining figure - and one acknowledged by Moore - is the pedimental figures of the Elgin Marbles. Kenneth Clark pointed out in The Nude (1954), three years after Moore had made his first visit to Greece, that two of the sculptor's finest reclining figures, one carved in stone (1938), the other in wood (1946), "develop two basic ideas of the nude which was first embodied in the Dionysis and the Illissus of the Parthenon - the stone figure with bent knee rising from the earth like a hill, the wooden figure with averted thorax and open legs, struggling out of the earth like a tree, not without a powerful suggestion of sexual readiness".
Younger British artists are no less fascinated by the Elgin Marbles. Jake and Dinos Chapman's Hell, a vast landscape sculpture shown in the Royal Academy's "Apocalypse" exhibition, features a ruined Parthenon-style temple, draped in fragments of Nazi banners. It is placed on a hill in a devastated landscape heaving with corpses and atrocities. The temple has a pediment frieze that shows Nazis in various states of decomposition and skeletons coming to life. The Nazis were obsessed with Greek culture, and their holy of holies was the Valhalla, a Bavarian version of the Parthenon in its complete state. But for the Chapman brothers, Greek culture is a ruin culture, and history is an endless dionysian cycle of creation and destruction: "Tragedy is written into the subject matter of Greek sculpture, and into its condition - the Elgin Marbles have not only been eroded, they've been blown up and scrubbed. They lend themselves to fractured notions of modernity."
During their stay here, the Elgin Marbles have been catalysts for a rich and varied harvest of art. Those who think they should be returned because they have been wasted on British artists need to think again.
James Hall is the author of The World as Sculpture (Pimlico, £15)