Sources and Identity
The whole of the documentary tradition for Marcellus of Trier rests on the September 4 entry of the Roman Martyrology, where he is named simply as bishop and martyr at Treves. No account of his episcopate, the manner of his death, or the persecution under which he suffered has come down, and his name is absent from the commonly cited lists of the bishops of Trier. He belongs, in consequence, to the large class of early martyrs whose veneration is securely attested while their history is effectively lost.
As with all entries of this kind, the bare martyrology notice is the limit of what can be responsibly asserted. The most that the calendar affirms is that a bishop named Marcellus was venerated at Trier as a martyr; the title Hieromartyr reflects this combination of episcopal rank and martyrdom.