Tertius
Never as well known as that other Roman numeral name, Octavius, Tertius just might hold some appeal for the parent seeking a really obscure name with the patina of antiquity for her third son.
Tertius was an early Christian and a scribe whp assisted Paul in writing his epistle to the Romans. In George Eliot's Middlemarch, Tertius Lydgate is an idealistic doctor.
