The Book of Dimma (TCD MS 59) is a small volume that contains the four Gospels as well as a few later additions, and was probably made in the late 8th century at Roscrea, a monastery founded in the 7th century .
Just as the Book of Mulling was not written by Mulling (see previous post), the Book of Dimma was not written by Dimma.
The name Dimma appears on several pages at the end of three Gospels (pp. 29, 52 and 148), but in each case it was written over an erasure. The reason for the alteration would have been to enhance the holy nature of the book by connecting it to an episode from the life of Saint Crónán (d. 619), the founder of the Roscrea monastery. According to the legend, Crónán asked a scribe called Dimma to produce a copy of the Gospels for him, demanding it to be ready by the next day. Dimma succeeded in this impossible task, as the sun miraculously did not set for the next forty days.
Whoever wrote the name of Dimma over that of the original scribe wished to transform this manuscript into the famous Gospels; the alteration was probably made at Roscrea in the late 10th or 11th century. Luckily, one colophon was left intact, on p. 103, revealing the original name of Dianchride, a name that occurs in the genealogy of the Uí Chorcrain, who had a branch based in the northern part of Tipperary.