Auxilius (Auxilinus, Ausaille, Usaille) (d. c.459), saint, missionary bishop and confrère of St Patrick (qv), was, according to one tradition, sent by Amatorex, bishop of Auxerre, to assist Patrick in his mission in Ireland and was later consecrated bishop by him. A ‘Lombardian’ origin has also been indicated (Ó Riain, Corpus geneal. SS Hib.). An early church dedication to him at Killashee (Cell Usaille), near Naas, Co. Kildare, would suggest that his sphere of missionary activity was mid Leinster. Later tradition associates him with Iserninus (qv), the third member of the Patrician triumvirate. His name survives in several different forms in the martyrologies, and each is given a separate feast-day. His chief feast-days are 19 March and 27 August (Mart. Drum.: Ausaille; Mart. Christ Church: Auxilinus, ‘discipulus et frater et coepiscopus scti Patricii’), and 16 September (Mart. Tall., Mart. Gorm.: Auxilius).
The strongest evidence for his association with Patrick comes from the inscription to a small collection of canons known as the second synod of Patrick, which survives only in a late ninth-century manuscript from Tours (Cambridge, Corpus Christi College 279). The inscription attributes the text to Patrick, Auxilius, and Iserninus, in that order. In the form in which we presently have it, the text is likely to be of seventh-century date, but it is clearly an ancient document, which prescribes rules for the governance of a Christian community in its formative stages; it may therefore possibly date to the period of Patrick's mission.