Sezin of Guic-⁠Sezni

Sezin of Guic-⁠Sezni was a bishop and abbot, honoured in Brittany as patron of the parish of Guic-⁠Sezni in Léon, in the fifth and sixth centuries. Little is known of him with certainty.

His life was compiled by Albert le Grand from the readings of an old breviary of Saint-⁠Pol-⁠de-⁠Léon, which are taken for the most part word for word from the life of Saint Kieran. According to this largely legendary account, he was born in Ultonia (Ulster) in 402, son of Ernut and Wingella; his mother is said to have had a vision of a star falling into her mouth. As a young man he is said to have retired to an island called Clare and, at twenty-⁠five, to have gone to Rome, where he met Saint Patrick, who presented him to Pope Celestine I; the pope consecrated him bishop to help in the mission to Ireland. O'Hanlon regards the part about the island as fictitious.

An ancient office in nine lessons was celebrated in the churches of Léon and Cornwall on 19 September. The day of 6 March is the one used by Colgan and the Bollandists; it follows the Julian calendar. He is honoured in the Breton and Irish calendars, with no synodal canonization shown in the source.