The Psalter of St Columba is a 6th century manuscript thought to be the first book written in Ireland.
The story goes that the manuscript was secretly copied by St Columba (Colum Cille) from a book he was lent, and St Finnian of Movilla, the lender of the original, claimed the copy should be returned to him as well. The Irish King Diamait judged that Finnian was in the right, which has been cited as the first instance of copyright law. The decision was so controversial it sparked a battle, and Columba was exiled to the island of Iona.
While the story may be apocryphal, the book became a holy relic in the keeping of Clan O'Donnell, who in the 11th century constructed an elaborate silver cumdach (book reliquary) to house it, and a tradition arose of carrying it three times around the O'Donnell warriors before a battle, gaining it the name "Cathach" or "Battler". It remained the property of the O'Donnells until 1843, when Sir Richard O'Donel entrusted it to the Royal Irish Academy.