Lismore Abbey was founded around 632 by Mochuda, in a picturesque site, steeply rising from the southern bank of the River Blackwater.
Its founder had spent nearly forty years of his monastic life in the monastery of Rahan on the southern borders of ancient Meath.
Irish annals tell us nothing of Cathaldus, because he went abroad early in life, but the brothers Morini of his adopted home provide some information.
thought that the ancient but now lost "Book of Cuanach", cited in the Annals of Ulster, but not later than A.D. 628, was the work of this Cuanna of Kilcooney and Lismore.
It was also a place of pilgrimage, and many Irish princes gave up the sceptre and returned to Lismore to end their lives in prayer and penance.
There, too, by his own desire, was interred Celsus of Armagh, who died in Ardpatrick, but directed that he should be buried in Lismore (though no trace of his monument has been found).