A former Cursor Callidus, Fidelias turns traitor to the Crown at the outset of Furies Of Calderon. He has an extensive knowledge of the Deeps below Alera Imperia. Fidelias, like most earthcrafters, also hates flying. He has the ingrained habit of checking anywhere he goes for the best route of escape.

During the event's of Cursor's Fury Fidelias is shown to be living under the guise of Valiar Marcus, the prime centurion of the First Alerian Legion. While the events of the war against the Canim played out, Fidelias found himself with conflicting loyalities once he discovered the true parentage of "Rufus Scipio", who was, in fact, Gaius Octavian, the heir to Alera.

He then began to play the role of traitor to Lady Aquitaine, while inside he had conflicting emotions which made him realize he needed to follow his heart and support the true heir to the realm, Octavian.

Fidelias has been named to two houses in Codex lore:

House of the Faithful carries the beginning name of Fidel- (Fidelias)

House of the Valiant carries the beginning name of Vali- (Valiar Marcus)