Classicism is timeless; the antithesis of "fad." Classically proportioned, designed and ornamented pieces will always contribute a timeless elegance to any room.
A newly made piece in an earlier style--say that of Louis-Philippe--a style which itself drew upon earlier classical motifs, can be as important to a successful room arrangement as any period antique piece. It's all in the proportion, the line and that unmistakable detail.
Piranesi's inventory reflects this mixing of the period piece and the classically designed contemporary piece.