Killian was an Irish monk who came to the continent in the great Irish missionary wave of the 7th century. With his companions Colmán and Totnán he established his mission at Würzburg in Franconia around 686, having received papal blessing for the mission from Pope Conon in Rome.
Under his preaching the Frankish Duke Gozbert of Würzburg accepted baptism. Killian then pressed Gozbert to put away his wife Geilana, whom he had married in violation of canon law (she was the widow of his brother). Gozbert was inclined to obey; Geilana plotted.
While Gozbert was away on a campaign, Geilana sent assassins to the Irishmen's hut. They were martyred on July 8, 689, beheaded together — Killian and his two companions — their bodies hidden in a stable. The deception was uncovered some years later when one of the assassins, dying mad, raved of the killing.
Their tomb at the foundation of the great Cathedral of Würzburg has been one of the principal Bavarian pilgrimage sites for thirteen centuries. The Würzburg Kiliani-Volksfest each July remains one of the largest religious-folk festivals in central Germany.