The very difference between ornament and structure is subtle and perhaps arbitrary. The pointed arches and flying buttresses of Gothic architecture are ornamental but structurally necessary; the colorful rhythmic bands of a Pietro Belluschi International Style skyscraper are integral, not applied, but certainly have ornamental effect. Furthermore, architectural ornament can serve the practical purpose of establishing scale, signaling entries, and aiding wayfinding, and these useful design tactics had been outlawed. And by the mid-1950s, modernist figureheads Le Corbusier and Marcel Breuer had been breaking their own rules by producing highly expressive, sculptural concrete work.