The foundation of the Hermitage is conventionally dated to 1764 when Catherine made her first bulk purchase of 225 paintings, including three Rembrandts, a Franz Hals and other notable Dutch works. Her influence is still detectable in virtually every gallery and department - she is the presiding spirit of Russia's greatest museum.
In a letter she wrote to Friedrich Melchior Grimm, a Parisian gossip and journalist, in 1790, six years before her death, Catherine was able to congratulate herself on having a collection that outclassed those of all other monarchs of her day. "Besides the paintings and the Raphael Loggia," she wrote, referring to her 4,000 Old Masters and her copies of frescoes Raphael painted for the Vatican Palace in Rome,
my museum in the Hermitage contains 38,000 books; there are four rooms filled with books and prints, 10,000 engraved gems, roughly 10,000 drawings and a natural history collection that fills two large galleries.
She forgot to mention her 16,000 coins and medals. For Catherine, the dinner service that she ordered from Wedgwood, decorated with 1,222 different views of British architectural monuments, was for use and not part of her art collection. In the same way she ordered services from Sevres, Meissen and St Petersburg, silver from the greatest silversmiths of Paris, and magnificent furniture from David Roentgen in Germany - Marie Antoinette's favourite cabinetmaker. All of these can also still be admired in the Hermitage galleries.
The museum takes its name from an extension that Catherine built on to her Winter Palace in central St Petersburg - a pavilion intended for private parties which she called her "Hermitage". As her art collection grew she had to build a second extension, the "Old Hermitage", and, finally, she added a theatre - the "Hermitage Theatre" - to this line of buildings which now stretches for almost a quarter of a mile down the banks of the River Neva. After the 1917 Revolution, the whole complex, including the Winter Palace itself, was allocated to the museum. Until the recent extension of the Louvre, the Hermitage was the largest museum in the world.
Catherine was not, of course, solely responsible for this magnificent institution. Peter the Great himself, who founded St Petersburg on the estuary of the River Neva in 1703, bought the museum's first Rembrandt. The costume department still owns 200 of Peter's clothes, including some of his underwear.
Catherine's son Paul couldn't stand the place, but her grandsons greatly embellished it. Alexander I, who fought against Napoleon, bought the cream of Empress Josephine's art collection which he carried back to the Hermitage. His brother Nicholas I encouraged the excavations in southern Russia which yielded the museum's incomparable Scythian and Greek gold artefacts. He also added the "New Hermitage" on to the back of the palace, a custom- built museum which he filled with the finest of the imperial collection and opened to the public in 1852.
Since the Revolution an Oriental department, an archaeological department and a Russian department have been added to the museum. There are now three million items in the collection, compared to one million in 1917 - of which only 5 per cent are currently on show. A vast expansion into nearby imperial buildings, used by the military since 1917, is now in the pipeline, ensuring that the Hermitage's future, like its history, will be spectacular.
Geraldine Norman is author of `The Hermitage: the biography of a great museum' (Pimlico, 4 February, pounds 12.50)