One of the world's oldest libraries, at the Vatican, is to close for three years for rebuilding, in an unexpected blow to scholars around the world.
The decision to shut the library was made without warning.
After the library closes for its summer break in mid-July, it will not reopen until September 2010, the Vatican says.
The reason is that some buildings constructed only a quarter of a century ago are now considered unsuitable for the safe storage of ancient books.
Air conditioning and dust protection will be installed and fire exits will be improved.
During the closure, scholars will still be able to obtain digital copies of ancient manuscripts in the Vatican library that they can study at home.
But the reading room, which is used by about 100 scholars a day, will be occupied during rebuilding by the Vatican's book restorers, who have to look after more than one million printed volumes and 75,000 priceless manuscripts.
Many of the books are stored in underground bunkers.
The Vatican library was founded by Pope Nicholas V nearly 600 years ago and has been open to scholars ever since.
There is another archive kept in the Vatican called the secret archive, which is not normally available to scholars.
This contains among other historic documents the love letters of England's King Henry VIII to Anne Boleyn, stolen by a Vatican spy to provide evidence for the pope when the king unsuccessfully sought an annulment of his marriage in Rome.