The Book of Dimma is an 8th-century Irish pocket Gospel Book originally from the Abbey of Roscrea, founded by St. Cronan in County Tipperary, Ireland. In addition to the four Gospels, in between the Gospels of Luke and John, it has an order for the Unction and Communion of the Sick. The surviving illumination of the manuscript is a number of illuminated initials, three Evangelist portrait pages, and one page with an Evangelist’s symbol.
A well-known legend relates that Cronan asked a monk named Dimma to copy the book, but that it had to be done in one day. Dimma set to work on this impossible task and copied continuously without a break for any meals. All the while he worked the sun never set. When Dimma finished, he thought that it had only taken him one day, when in reality it had taken forty. This miracle was attributed to Cronan.
In the 12th century the manuscript was encased in a richly worked cumdach or reliquary case, which remains with it at Trinity. On one face it has panels of openwork decoration in Viking Ringerike style over the wood case. There is a good reproduction of 1908 in the Metropolitan Museum of Art in New York, which is not on display there, but has good illustrations available online, unlike the original piece.