The two-volume prayer book – known as the Aberdeen Breviary as it was commissioned by the Bishop of Aberdeen – was the first service book to chronicle the lives of the Scottish saints when it was printed in 1509-10.
Experts believe the creation of these volumes was the reason King James IV granted the first printing licence in Scotland in 1507 to Walter Chepman, who owned the nation’s only printing press.
Concealed at the back of the Breviary is the only known copy of a 16-page booklet called the Compassio Beate Marie.
This small book, which contains orders of service and readings about the arrival of St Andrew’s relics in Scotland, is the most unique example of early Scottish printing to be added to the National Library collection in 200 years.
The Compassio was printed between 1510 and 1532, providing clear evidence that the Scots continued to print their own books after producing the Breviary.
Helen Vincent, head of rare books at the National Library, said: “We are delighted to have brought these hugely important examples of early printing in Scotland into public ownership where they will be made widely available for study for the first time.”
The Aberdeen Breviary has been kept in the Earl of Strathmore’s library at Glamis Castle, in Angus, for many years and was offered to the National Library by Christie’s auction house, which is acting on behalf of the estate’s trustees. Known as the Glamis Breviary, it was the only remaining copy in private hands.
There are three other surviving copies of the prayer book but the Glamis copy is considered to be the best example by scholars as scrawled on to the pages are contemporary annotations, including sets of verses and music.
The library would not confirm the cost of the books, which are believed to be worth six figures.
Alan Grant, owner of Grant and Shaw booksellers in Stockbridge, said: “It is an exceedingly rare book. It must be one of very few in existence. You could safely put a six-figure sum on it.”
The volumes are written in Latin and the library plans to create a modern translation of the text as there has never been a full version before.
Scotland’s national librarian, Dr John Scally, said: “This is a very significant addition to our collection.
“Each surviving copy of the Aberdeen Breviary makes an important contribution to our understanding of how Scotland’s first books were printed.
“As is often the case with the first products of a printing press, the work was still somewhat experimental and many corrections were made during the printing process.
“The Aberdeen Breviary is the only work which allows comparisons to be made, shedding new light on Scotland’s first experience with printing.”