The Pontifical has been associated with Bangor Cathedral for almost 700 years
A precious 700-year-old manuscript will be on view at Bangor Cathedral for one day when a service is held to celebrate its return to the city.
The Bangor Pontifical is a 14th Century bishop's manuscript, containing blessings and text of plainchant.
It has recently been conserved and rebound, but will now be kept for safety in Bangor University's archive.
A service on Sunday will include several plainchant melodies newly transcribed from the document.
The manuscript, which contains music notation and Latin text for services conducted by a bishop throughout the year, can also be seen online.
It includes instructions and the text to be used for bishop to dedicate churches, altars and cemeteries, as well as blessings.
Dr Sally Harper from Bangor University explained: "We've had the book digitised by a specialist team from Oxford and you can actually see every page in glorious detail on the website which we are now developing.
"We're going to have parallel translations of the Latin text and there will also be musical notation and sound files.
"So you'll be able to click on a melody and hear it."
The document has been inscribed as belonging to Anian, who was bishop of Bangor between 1309 and 1328.
The bilingual service starts at 1515 GMT and is open to all
The Pontifical will be received on Sunday by the Dean of Bangor, the Very Rev Alun Hawkins, and blessed by the Bishop of Bangor, the Rt Rev Andrew John.
The service has been devised for the occasion by Bangor University's International Centre for Sacred Music Studies in collaboration with the cathedral.
Music will be sung by the cathedral choir, an all-female schola from the university, and a professional cantor.
The service also includes readings from the medieval Life of St Deiniol, patron and Bishop of Bangor, whose monastery stood on the site of the present cathedral.
The Pontifical will be blessed in the words of a medieval benediction.
Funds raised by the cathedral and university paid for the manuscript to be digitised and for the National Library of Wales, Aberystwyth, to conserve the original.