Nazi Germany built prolifically. It also proscri-bed prolifically. Among its antipathies was Expression-ism, which, pace the dicta of countless architectural historians, was still flourishing in the north of the country when the NSDAP (Nazi Party) came to power in January 1933. International Modernism was decried as Communist, Expressionism reckoned indulgently individualistic.

Yet the built legacy of the 12-year Reich consists predominantly not of Classical bombast, nor even of völkisch cottages, but of approximately 60,000 defensive structures whose forms go way beyond the functional. They manifest a sculptural brawn that is often coarsely ‘legible’: their forms recall animals, reptiles and visors, whose message is that they are merciless jailers watching over the population of the occupied countries.

The Organisation Todt built many more Expressionistic structures than the Expressionists did; it gave the idiom new legs. The Atlantic Wall stretched from the Barents Sea to the Pyrenees, the West Wall from Kleve near Arnhem to the Black Forest, and the Südwall from France’s Span-ish border to the Italian.

They include U-boat pens, missile-launching sites, gun emplacements, subterranean bunkers, watchtowers, flak towers, bomb silos and so on. Unlike Nazi gifts to the world such as space travel, the Volks-wagen and all things Green, these cumbersome, sometimes awesome lumps of concrete retain the power to discomfit us.

They are unequivocally belligerent. They were built for a tyranny by workers who suffered different degrees of slavery and by conscripts of STO (Service du travail obli-gatoire). No matter where they are to be found, they always look out of place. In urban settings-Hamburg, Vienna-their freakish size is impressive: imagine an 0-scale model dropped into an 00-scale streetscape.

 

For about two decades after the war, no one took much notice of them. At Noirmoutier, and no doubt elsewhere, they were converted into primitive holiday homes. Then, the French urban theorist Paul Virilio began to photograph them. His project would culminate in the mid-1970s in Bunker Archaeology, a book that opened a debate.

What ought to be done with them has taxed historians, environmentalists, museum people, tourist boards and bunkerologists (they do exist) ever since.

Virilio also established a template for future, more technically adept photographers, such as Peter Mackertich, who works in stern monochrome-the war was, of course, fought in black and white. Monochrome lends bunkers a sort of lugubrious authenticity, an immaculacy (if one can use such a word in this context). It maintains the satanic etiquette that attaches to them. Their original purpose is proclaimed unambiguously. Seventy years have not dissipated the terror.

Ianthe Ruthven’s take on these sites could not be more different. She is a kind of apostate. Her palate is saturated and polychromatic. Her big digital prints are gaudy celebrations of the disrepectful trashing that Organisation Todt’s work has been subjected to. They show 7ft-thick concrete walls tattooed with graffiti, which, of course, diminishes the integrity of the structures.

The desecration ought not to concern us: the mildly antisocial behaviour of kids in Nikes with spray cans and a certain gift is nothing beside the vile behaviour of kids in helmets with Mauser submachine guns and a murderous ideology.

Ianthe’s work derides the defaced structures it shows. The once mighty are long dead (by their own hand, mostly). Now, they are turning in their graves as their monuments to boorish belligerence and racial supremacy are mocked by Nature as well as vandals. Mockery is powerful. It does not accept people or dogma on their own terms. It ridicules them. Here, dour grey concrete is rendered playful or detoxified by nature’s exuberance. Nazi ruins can hardly be said to be causes for optimism. Yet when the physical remnants of a terrible regime are divorced from their purpose, the weight of the past is lifted from us.

The evident danger is that the ahistoricism of Ianthe’s novel approach and her disregard for context might encourage us to forget what caused the structures to be built, in the way that we have forgotten, if we ever knew, what Stonehenge and Callanish were actually for.

But, given the way that Hitler and his works are routinely rammed down our throat, that is improbable and there is, anyway, something bracing about the way in which he is posthumously ridiculed by a weapon no more lethal than a camera.There is a kinship of spirit with John Heartfield’s entirely irreverent photomontages of the years immediately before the Nazi seizure of power. That is high praise.

‘The Atlantic Wall: Hitler’s Coastal Fortress from the Arctic to the Pyrenees’ is at the Royal Geographical Society, 1, Kensington Gore, London SW7 until June 20 (020-7591 3000; www.rgs.org; www.iantheruthven.com). A book of the same name accompanies the exhibition

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