The bishop, alternately known as Illidius or Allyre, is credited with helping Clermont-Ferrand become an important center of monastic culture and religious teaching—probably one of the reasons it was chosen by Pope Urban II for announcing the First Crusade.
Illide supposedly cured the daughter of Emperor Magnus Maximus of Rome. His reputation earned him praise from Gregory of Tours.
Illide died in 385. His feast day is 7 July (except in Clermont, where they celebrate him on 5 June.)