French architect and theorist Viollet-le-Duc (1814-1879) spent more than half of his career restoring Gothic-era castles, cathedrals, and public buildings, including such notable projects as Notre Dame de Paris and the city walls of Carcassonne. Yet he’s often seen as a pre-modernist, influencing Henry van de Velde and even Frank Lloyd Wright. Viollet-le-Duc’s theories of...