Ferdomnach (d. 845) was chief scribe of the monastery of Armagh in the first half of the ninth century and scribe of the Book of Armagh. Although an unprinted genealogy of Ferdomnach, tracing his descent back twenty-three generations, is preserved in the Book of Lecan, nothing certain is known of his ancestry nor of his career other than that he was the main or possibly the only scribe of that monumental work of Irish calligraphy and scholarship, the Book of Armagh (‘Liber Ardmachanus’ or ‘Canóin Phátraic’, as it was later known). In addition to the celebrated Patrician documents and hagiographical material, the manuscript includes the only surviving copy of the New Testament from the pre-Norman Irish church.
Ferdomnach left his subscriptio in four places in his masterpiece: at the ends of the gospels of Luke and Mark (both of them now almost illegible); at the end of Book II of Muirchú's Life of St Patrick (qv); and at the end of the epistle of Sulpicius Severus – the latter two read ‘pro Ferdomnacho ores’ (pray for Ferdomnach). In 1846 Charles Graves (qv) brilliantly deciphered a colophon in a debased Greek uncial, now somewhat abraded, at the end of Matthew's gospel (f. 53va), which reads: ‘[Ferdomn]ach hunc [libru]m . . . e dictante . . . bach herede Patricii scripsit’; on substituting Latin characters for the Greek, he deciphered it as: ‘Ferdomnach wrote this book . . . at the dictation of (Tor)bach, heir of Patrick’. The Annals of Ulster for the year 808 record the death of ‘Torbach, a scribe, abbot of Armagh’. Torbach (qv) had been abbot of Armagh for only one year in 807, and was the only holder of the office with that name. Another colophon, also at the end of Matthew, states that Ferdomnach had completed that text on the feast of Matthew, thereby dating his transcription of that portion of the manuscript to 21 September 807.
The Book of Armagh is written in a very fine Irish minuscule throughout. The external appearance of the handwriting and the arrangement of the text on the page varies with the subject-matter and with the scribe's own disposition, at times becoming so ornate as to be difficult to read. The manuscript, which originally had 222 folios, may then have been bound into a number of smaller volumes. It was encased in a cumtach or book-shrine in 937. The manuscript is now held in the library of Trinity College Dublin (MS 52). It is probable that at one time many other specimens of Ferdomnach's calligraphy existed, but only the Book of Armagh is now extant.
Ferdomnach's death is recorded in the Annals of Ulster at 845: ‘a learned man and excellent scribe of Armagh’. It is possible that he had retired to Clonmacnoise some time before his death, as a ninth-century cross-slab inscribed with the name ‘Ferdomnach’ was discovered there by George Petrie (qv) in the early nineteenth century.