Adomnán (qv) in his ‘Vita Columbae’ refers to Mauchteus in the words: ‘For it is an accepted fact passed down to us from ancient men who knew of it that a certain British stranger, a holy man, a disciple of the holy bishop Patrick, called Maucteus, prophesied thus of our patron, saying: “In the last years of the world a son will be born, whose name Columba will become famous through all the provinces of the islands of the ocean, and will brightly illumine the latest years of the earth. The fields of our two monasteries, mine and his, will be separated by the width of one small hedge: a man very dear to God, and of high merit in his sight.” The similarities between the annal obit and Adomnán's reference to ancient tradition make it quite probable that both are drawing upon some genuine sixth-century source, possibly a letter of Mauchteus or an old annal entry. Indeed, his obit may derive from the annals believed to have been recorded on Iona. These references are therefore an important witness to the link between St Patrick and the sixth-century Irish church.
Some sources give Mauchteus an impossible lifespan of three centuries, while others grant him a span of 120 years, also stating that the last rites were administered to him by Daig (qv) (d. 587) of Iniskeen. His feast-day is given variously as 19/20 August and 24 March. For some unknown reason, some antiquarians, such as Bale, have identified him with the early fifth-century Spanish author Bachiarius; curiously, the only copy of the ‘Fides Bachiarii’ exists in a seventh-century Irish manuscript, that was possibly written at Bobbio (Milan, Bibl. Ambro. O.212 sup.).