Ercnait (5th/ 6th cent.?), foundress of Dún dá Én and saint in the Irish tradition, belonged to the Cruithin lineage of Uí Nialláin, located in the vicinity of Armagh in what would later be the overkingdom of Airgialla. She belongs to the first generation of Irish religious women and is closely associated with St Patrick (qv), who is believed to have given her the veil. Her father is identified as Dáire son of Findchad, the dynast credited with donating a place called Druim Sailech (an alias for Armagh, later the site of the principal Patrician church) to Patrick. Patrician tradition maintains that Ercnait travelled in Patrick's retinue along with other virgins including Lupait and Cruimthiris. It is related that she fell in love with the young monk Benignus (qv), and Patrick, anxious to preserve her vow of chastity, arranged for her to die and be resurrected free from sexual desire – a motif to account for her ‘rebirth’ to a new spiritual life.
Ercnait was sent to the hermitage of Tamlachta-bó (Tamlaght, parish of Eglish, Co. Armagh), although her principal foundation was later regarded as that of Dún dá Én in Dál nAraide (Duneane, Co. Antrim). There are chronological difficulties in identifying this Ercnait with a holy woman so named who allegedly helped the virgin Cóch to establish Cell Chóca (Kilcock, Co. Kildare), and who is said to have been robemaker to St Colum Cille (qv) (d. c.597). It is possible, however, that Patrician and Columban traditions concerning a saint named Ercnait may reflect conflicting claims on her foundations in the tenth century or later. Her death is commemorated in the martyrologies at 8 January; it should probably be dated to the early sixth century. A separate entry at 30 October may relate to the translation of her relics.