A former Cursor Callidus, Fidelius turns traitor to the Crown at the outset of Furies Of Calderon. He has an extensive knowledge of the Deeps below Alera Imperia. Fidelius, 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 event's of the war against the Canim played out, Fidelias found himself with conflicting loyalities once he had discovered the true parentage of "Rufus Scipio" who was in fact Gaius Octavius the heir to Alera.
He then began to play the role of traitor to Lady Aquinitius while inside he had conflicting emotions which made him realise he in fact needed to follow his heart and support to the true heir to the realm.