Architecture: Bath: secrets behind the Georgian facade: Some say it was jerry-built, but how come so many treasures survive? Frank Barrett visits a museum that houses the answers

Christopher Woodward, curator of the Building of Bath Museum, admits to his own Georgian building fantasy. As he peruses the collection of rare books housed in the newly opened Sainsbury Study Gallery of the museum, he articulates his dream.

'What I would really like to do is build a Georgian house here in Bath in the way that the houses were originally built 200 years ago. It would be easy to find a plot, and people could come along and see how the whole thing was actually done.'

The Building of Bath Museum, now in its second year, reveals most of the secrets of the Georgian builders through a series of ingenious exhibits. There are some aspects of construction, however, that continue to baffle historians. 'For example, we don't really know how they managed to manoeuvre the heavy Bath stone blocks up the scaffolding.'

Among the rare books are plenty of Georgian building manuals, offering advice on construction and design. A bound volume of Builder's Magazine for 1788 contains finely detailed plans for every sort of dwelling the Georgian man and woman about town would have desired: everything from a 'two up, two down' to a mighty Gothic castle. (The castle illustrated is Midford Castle - coincidentally the home of Michael Briggs, the chairman of the Bath Preservation Trust, which runs the museum.)

Other volumes in the museum's collection include a book of tables used by 18th-century builders to calculate their charges; and for those who had the task of checking the fine details of Ionic columns and the exacting proportions of classical facades, the lavishly illustrated Pocket Treasures, which the builder could slip into his pocket and consult at the top of a ladder.

Mr Woodward says: 'It's astonishing that the myth has persisted that Bath was jerry-built. When the properties were constructed they were sold on a 99-year lease, and the feeling has grown up that the builders more or less threw the buildings up, not caring if they stood for much longer than the contracted 100 years.'

In fact, the exhibits in the Building of Bath museum - a delightful full-size working model of a sash window, for example - make it clear that while builders had to be economical with expensive Bath stone, the houses were built with extraordinary care and attention. Compared with the cost of stone, labour was cheap, and on-the-job deaths were common.

The front walls of the houses, on which a disproportionate amount of care was lavished, are sometimes nothing more than a slender skin of ashlar. It is a tribute to the skill of the masons that such a sturdy construction was founded on such slender support.

'After 200 years, the Georgian houses of Bath are still in good condition. I would say that if they've been standing for 200 years, they'll be good for at least another 200,' Mr Woodward says.

It is a testament to the soundness of the Georgian builders' work that of the 7,000 houses built during Bath's heyday, from 1714 to 1830, more than 5,000 remain. The rest disappeared not as a result of shoddy workmanship, but because of the attentions of the developer's bulldozer. The notorious 'Rape of Bath' during the Fifties and Sixties, and the property blight caused by the bizarre Buchanan plan to put a traffic tunnel under the city, took a heavy toll on Bath's architectural heritage.

Christopher Woodward, standing beside the museum's huge scale model of the city, points out the areas worst affected. 'The houses knocked down were mostly artisan terraces - no grand buildings were touched.'

It is now extraordinary to think, however, that as little as 30 or 40 years ago the city's fathers were happy to demolish rows of intricate and intimate Georgian houses to make way for immense and ugly council flats.

Despite the work of the demolishers, Bath remains the most complete Georgian city in Britain. It was the first planned city outside London, unique with its arrangement of square, circus and crescent all built to John Wood's plan, and each one an architectural innovation. Wood's Circus was the first, from which all the others were developed.

John Wood the elder (his son, John Wood the younger, completed the job) was a legend in his 18th- century lifetime. Born as a lowly builder's son, he went to London, taught himself architecture and returned to Bath to win something worth more than a fortune in those days: a place in high society.

It is a surprise, therefore, to discover that in some ways he was a few ashlar blocks short of a pediment. He was convinced that Bath was a druidic city, founded in pre- Roman times by the mythical English king Bladud, father to King Lear. He was also of the opinion that the Greek god Apollo used Bath as his summer residence, being wont to frolic on the river meadows next to what is now the Sainsbury's building in Green Park.

Wood's druidic beliefs were incorporated in the design for his Circus, which was built to the exact dimensions of the stone circle at Stonehenge.

Surprisingly, it is only recently that Bath's Georgian houses have become very expensive. A grand house in New Sydney Place when it was built in 1808 would have cost pounds 1,600, which was expensive - about as high a price as houses reached in Bath at that time, Mr Woodward says. It wasn't until the Fifties that this same house was once again worth as much as pounds 1,600. Today Mr Woodward estimates that it would be sold for about pounds 800,000.

No doubt John Wood would find this hard to believe - harder even than the idea of Apollo popping into the local Sainsbury's for a bottle of retsina.

(Photograph omitted)