Architecture: Fonthill: a house that haunts: It was the marvel of its day, until it came crashing down. But the magic lives on, says Jonathan Glancey

Fonthill Abbey has haunted me since when, as a short-trousered, snake-belted child, I saw its astonishing image reproduced in a dog-eared and tea-stained library book. I so wanted to see this house - a fantastic Gothick abbey owned by a fabulously wealthy recluse - that it became the stuff of my dreams and one of the reasons I came to love architecture.

What I did not know - I could not read architectural histories then - was that this romantic pile survived not in concrete, stone and stucco, but in regency engravings pressed into Quarto India paper. Fonthill Abbey had existed, but only for a very short while. It was designed by the gimcrack architect James Wyatt and built between 1796 and 1822. Wyatt's patron was William Beckford (1760-1844), 'England's Wealthiest Son', grand tourist, orientalist, Member of Parliament, author of Vathek (the Gothick horror novel), radical and recluse.

Fonthill was the stuff of legend in its day and much admired by the great romantic painters Constable and Turner. Walled and girdled round and closed to visitors, it intrigued the regency public; so much so that when Beckford first put it up for sale through Christie's in 1822, between 600 and 700 people a day traipsed through its soaring mock-medieval halls, gawping up to the plaster vaulting at the top of its wobbly 145ft tower. In all, at least 7,200 people paid a guinea each for a catalogue that gave admission to the abbey. It was the Disneyland of its day, Cinderella's castle writ uncannily large.

Beckford, however, was a decidedly canny soul. Deluged by debt - after the collapse of the West Indian sugar market from which he enjoyed his fortune - he sold the abbey and much of its contents to the Scottish gunpowder millionaire and collector John Farquhar for pounds 300,000. Fonthill had cost him about half of that to build and it had never really been completed. Architect and patron also knew that the shoddy concrete and weasel-thin construction would never last.

Farquhar was in his new home the night the tower fell down during a howling storm. That was in December 1825, only three years after the Scot had bought the abbey; small wonder that he died of apoplexy soon afterwards. The ruins of Fonthill were cleared away, so that today, traces of the once great Wiltshire house are next to invisible.

Beckford moved to Bath and commissioned H E Goodridge, a local architect, to build him a new 154ft tower overlooking the city in a part-Italianate, part-Grecian style (the lantern capping the tower is modelled on the Choragic monument of Lysicrates, Athens). Beckford died here in 1844, but the tower, unlike Fonthill Abbey, still stands.

Today, you can visit Beckford's Tower, and there is good reason to. An exhibition, 'Souvenirs of Fonthill Abbey', has been organised by the Beckford expert Jon Millington. Comprising a glorious collection of prints, drawings, ceramics, books, catalogues, souvenirs and other regency memorabilia, it documents the British public's fascination with this, the greatest - and most flawed - of all Romantic Movement houses.

In August and September 1822, after Beckford put the abbey up for sale through Christie's, 'Fonthill fever' gripped the nation. Clutching such popular guidebooks as Rutter's A Description of Fonthill Abbey and Demesne, a stream of visitors walked the length - all 312ft of it - of the vista that ran uninterrupted from the front door to the chapel of Beckford's favourite saint, Anthony of Padua. They gawped at the unrivalled scale of the house and its magnificent collection of paintings, books and furniture.

Cunningly, Beckford cancelled the sale, having whetted the nation's appetite. He knew that by stirring up 'Fonthill Fever' he would find a buyer desperate to pay over the odds for the house the nation so wanted to see.

A year later, he instructed that the house be put up for sale by auction a second time. Again, the crowds came. More than 7,000 tickets were sold during September and October 1823. Such was the rush that the Times reported: 'He is fortunate who finds a vacant chair within 20 miles of Fonthill; the solitude of a private apartment is a luxury which few can hope for . . . the beds through the county are doing double duty - people who come in from a distance during the night must wait to go to bed until others get up in the morning . . . not a farmhouse - however humble - not a cottage near Fonthill, but gives shelter to fashion, to beauty, and rank.' Beckford, ever solitary, hid away at his home in Lansdown Crescent, Bath during the ballyhoo.

Though so many people came to see Fonthill in 1822-23, there had been few visitors before. For all its chimerical beauty, Fonthill Abbey was a lonely place. A social outcast since a scandal in 1784 over alleged homosexual acts (a capital offence at the time), Beckford steered a lonely path through fashionable society. Those who did enjoy visits to Fonthill were social outcasts themselves, most famous among them Admiral Nelson, Hero of the Nile, and Emma Hamilton, who stayed here for Christmas 1800 and, frowned upon anyway, were widely criticised for doing so.

The collapse of Fonthill Abbey only added to its mythical status. Beckford had originally commissioned Wyatt to build a Gothick ruin, but he changed his mind and, demolishing the handsome Palladian-style house, Fonthill Splendens, his father had built, plumped instead for the most romantic and reckless house of its or almost any other day.

Today, Fonthill lives on in guidebooks, on Staffordshire bone china plate, Worcester vases, watercolours, lithographs, magazines and architectural histories. Its spirit was replicated to some extent in Beckford's tower at Lansdown, but more literally in the design of Hadlow Castle, Kent, which boasts a cut- down replica of the tower at Fonthill. But, mostly, this unlikely house survives in the realm of the imagination, where it had always belonged and, perhaps, should have stayed.

'Souvenirs of Fonthill Abbey', until 30 October, at Beckford's Tower, Lansdown, Bath. Open on Saturdays, Sundays and Bank Holidays, from 2-5pm. Other times by arrangement. Admission pounds 1.50, concessions 75p. Further details: Bath Preservation Trust 0225 338727.

(Photographs omitted)