(6th cent.)
[Venerated in Brittany, patron of the parish of Guic-Sezni, in the
diocese of S. Pol-de-Léon.]
Of this abbot nothing certain is known. Colgan attempted to identify
him with S. Isserninus, the companion of S. Patrick. According to
Albert le Grand, S. Sezin was born in Ulster, in 402, studied at Rome,
became a bishop in Ireland, and passed into Brittany in 477, where he
died as late as 529, having lived 127 years. But the lections in the
Breviary of S. Pol de Léon, from which Albert le Grand made up this
history, are for the most part taken word for word from the Life of S.
Kieran. We may allow that the saint was an Irishman, and that he died
at Guic-Sezni, in the beginning of the 6th century, but that is all we
can say of him.