This article presents, as a case study, the various inconsistencies which occur in the prosopographical entries concerning Simplicius, one of Sidonius’ most frequent addressees. Through the exegesis of passages of letters addressed to him (Epist. 3.11, 4.4, 4.7, 4.12, 5.4) and of passages believed to concern him (Carm. 24.89; Epist. 2.9 and 5.7), it argues for a revision of the common identification of Simplicius as brother of Apollinaris and Thaumastus, and for a re-evaluation of the sources which supposedly lead to this conclusion. Some cautionary remarks on the unchecked use of prosopography as a tool are followed by a hypothesis concerning the identity of this addressee of Sidonius.
