A cumdach or book shrine is an elaborate ornamented box or case used as a reliquary to enshrine books regarded as relics of the saints who had used them in Early Medieval Ireland. They are normally later than the book they contain, often by several centuries, typically the book comes from the heroic age of Irish monasticism before 800, and the surviving cumdachs date from after 1000, although it is clear the form dates from considerably earlier.
The usual form is a design based on a cross on the main face, with use of large gems of rock crystal or other semi-precious stones, leaving the spaces between the arms of the cross for more varied decoration. Several were carried on a chain or cord, often suspended round the neck, which by placing them next to the heart was believed to bring spiritual and perhaps medical benefits. They were also used to witness contracts. Many had hereditary lay keepers from among the chiefly families who had formed links with monasteries. Most surviving examples are now in the National Museum of Ireland.
Only five early examples survive, including those of the Book of Dimma and Book of Mulling at Trinity College, Dublin, and the Cathach of St. Columba and Stowe Missal at the Royal Irish Academy. Only the cumdach for the Gospels of St Molaise survives, while the book is lost, but more often the reverse is the case. Other books such as the Book of Kells, Book of Armagh and Book of Durrow are known to have once had either cumdachs or treasure bindings, or both, but with their valuable precious metals they were a natural target for looters and thieves. The church in Ireland emphasised relics that were, or were thought to be, objects frequently used by monastic saints, rather than the body parts preferred by most of the church, although these were also kept in local versions of the house-shaped chasse form, such as the Scottish Monymusk Reliquary. Another Irish speciality was the bell-shrine, encasing the hand bells used to summon the community to services or meals, and one of the earliest reliquaries enshrined the belt of an unknown saint, and was probably worn as a test of truthfulness and to cure illness. It probably dates to the 8th century and was found in a peat bog near Moylough, County Sligo.
Cumdachs are to be distinguished from the metalwork treasure bindings that probably covered most grand liturgical books of the period. However the designs may well have been very similar; the best surviving Insular example, the lower cover of the Lindau Gospels in the Morgan Library in New York, is also centred on a large cross, surrounded by interlace panels. Treasure bindings were metalwork assemblies tacked onto the wooden boards of a conventional bookbinding, so essentially the same technically as the faces of many cumdachs, which are also attached with tacks to a core wooden box.