The London that moved Wordsworth to put pen to paper on Westminster Bridge was captured in this splendid panorama. Hidden in a New York attic for years, it has now been returned to its home town.
Back in 1941, a housewife in Rhinebeck, New York, was cleaning out the attic of her late uncle's house. Inside an old gunpowder barrel stowed in a musty corner, she discovered this panoramic watercolour, which is more than 8ft long. The four panels form an extraordinary image of London, painted by unknown artists sometime between 1807 and 1811: a view of George III's capital city, made from the vantage point of a hot-air balloon. A work of remarkable accuracy and detail, in which a world of tiny events is taking place: kite-flying, a street brawl, ladies of quality taking their morning constitutional, bakers' men with trays of bread balanced on their heads.

The panorama is the work of several hands, but its similarity to Robert Havell Junior's 1831 Aeronautical View of London suggests he may have been involved in its production.

The piece was bought last year at Sotheby's for pounds 199,500, with money from the Heritage Lottery Fund, the National Art Collections Fund and the Victoria and Albert Museum. After 18 months of restoration, it has just gone on show at the Museum of London.

"It's a social document of a particular historical moment," explains Dr Lucy Peltz, assistant curator of paintings at the museum. "It depicts both the fashionable and commercial life of London, at a time when the country was isolated, but growing in economic strength." It was isolated, of course, because of the political disagreements between France and England that would be settled at the battle of Waterloo in 1812. If only Napoleon had seen this painting: to have London at his feet in panorama form might have been some consolation for his defeat.

A city laid bare

Some elements of the panorama are stylised: the perspective has been forced, to fit the city into the frame, and the blueness of certain church spires serves to direct the eye towards buildings of the greatest historical interest. On the left, notice the factory fire raging in Bermondsey, the funeral taking place at St John's churchyard in Southwark, the distant shape of the pagoda at Kew Gardens. Towards the right, there is a man firing a cannon on Brass Mount Battery at the Tower of London, sailors begging with a model boat and a man flying a kite over Tower Hill.