According to his apocryphal Acts, attributed to St Ambrose of Milan, he was a soldier who enlisted in the Roman army around 283. Diocletian, unaware that he was a Christian, appointed him as a captain of the Praetorian Guard. When he treated Christian prisoners due for martyrdom kindly, Diocletian reproached him for his supposed ingratitude and ordered him executed by arrows.
This method of execution made Sebastian a favourite for paintings. Sebastian is usually depicted in art as a somewhat effete youth tied to a stake and transfixed by several arrows. Sebastian was formerly one of the Fourteen Holy Helpers until that cult was suppressed in the reform of the Roman Catholic liturgy in 1969. Sebastian's own feast day is January 20.