Arts: How to ruin a building

The greatest aspiration that architect Sir John Soane had for his works was that they should tumble down.

Sir John Soane finished his massive reconstruction of the Bank of England in the mid-1820s. To celebrate the completion of his masterpiece, a great cutaway axonometric watercolour was displayed at the Royal Academy. Perhaps surprisingly to the 20th-century mind, Soane chose to portray his achievement as a fabulous classical ruin. Soane's contemporary and assistant, the artist Joseph Gandy, painted a Bird's-eye View of The Bank of England which reveals the building's labyrinthine interior, "like a meat pie with the crust removed". It is a watercolour which goes some way in illustrating just how carried away pre-Victorian society had become with the idea of ruins and ruination.

Soane himself had been taught at school that London was the new Rome. Historians and antiquarians were constantly pondering this question: if Englishmen had taken such inspiration from visits to the archaeological sites of the ancient world, would future scholars descend upon London after the collapse of the British Empire to visit and muse upon her noble ruins? Soane thought they would. During the early decades of the 19th century, hand in hand with the upsurge in Evangelicalism and Millennialism, artistic and literary images of ruins flooded the market.

Four years before his death in 1837, Soane handed over to a more bemused than grateful nation his uniquely eccentric house in Lincoln's Inn Fields, London. There was a condition that it be kept in the exact state in which he had left it, but deep down he felt that eventually the house would fall into ruin.

Earlier in his career, he had written one of the oldest documents in English architectural history, Crude Hints Towards an History of My House, which is transcribed in full for the first time and reproduced in the catalogue for a new exhibition at Sir John Soane's Museum entitled "Visions of Ruin: An exhibition of Architectural Fantasies and Designs for Garden Follies". In it he speculates on how his home would be inspected as a potential future ruin. Would the space-age antiquary interpret it as a Roman temple? A burial site? A convent? A monastery? A magician's lair? The house in Lincoln's Inn may be all or none of these things. Visitors to the exhibition can assess it for themselves and come to their own conclusions.

Quite by chance, I arrived to view "Visions of Ruin" at the same time as a party of beautifully turned out young ladies who were visiting from a seminary in Mississippi. I was therefore privileged to hear the curator of the exhibition, Christopher Woodward, expounding to them on the underlying complexities and contradictions of this theme.

Woodward has here assembled a fine collection of drawings and paintings, plans and perspectives of built and unbuilt works - fantasies and fine art from the likes of Batty Langley, Giambattista Piranesi, Robert Adam and William Chambers as well as Soane and his group of assistants. Together, they constitute a pot-pourri of architectural miscegenation. Here's a temple of Modern and Ancient Virtue, there a sham gothic castle at Wimpole Hall. Over here, Piranesi's representation of an undergrowth-entangled semi-circular exedra at Hadrian's Villa near Rome. And there, Soane's preliminary sketches for the outworks at his garden at Pitshanger. One and all of these caprices are, of course, depicted as ruins, stone remains, or - in the words of Francis Bacon - "remnants of history which have (by chance) escaped the wreck of time".

One of the most extraordinary exhibits (as powerful an image today as when it was first shown - and caused a sensation - in 1819) is a mezzotint owned by Soane of an original painting by John Martin of The Fall of Babylon. Based on text by Herodotus, the Book of Jeremiah, and contemporaneously written topographical descriptions, this work would make a splendid poster for an epic Cecil B de Mille blockbuster. It is worth the visit (and the pounds 2 entrance fee) for a glimpse of The Fall of Babylon alone.

As well as digging deep into the Soane's own extensive holdings, Woodward has trawled the archives of the Royal Institute of British Architects' library, the Royal Collection and the National Trust, and begged and borrowed from the late Sir Brinsley Ford, the trustees of the V&A and those delightfully named "Syndics" of the Fitzwilliam Museum in Cambridge.

Although the exhibition takes up very little physical space (fitting snugly into Soane's dining room), one could quite easily spend the whole morning savouring the rarities, contemplating the riddles, theorising on the paradoxes and metaphors, or merely reflecting quietly on the abstruse aesthetics.

"I don't understand any of it," a nine-year-old little girl with pigtails cried as her mother dragged the child from case to case, determined to ram it all down her throat whether she understood it or not. Beware. "Visions of Ruin" makes intellectual demands that would challenge graduate students in architecture and history of art.

Dulce est despere in loco, the poet Horace suggested at one stage. It is pleasant to be nonsensical in due place. Some of these follies and fantasies are about as nonsensical as it is possible to get. They'll help shake the summer madness from your head.

"Visions of Ruin", Sir John Soane's Museum, Lincoln's Inn Fields, London WC1 until 28 August. `Sir John Soane' will open at the Royal Academy, Burlington House, Piccadilly, London W1 on 11 September