The roof shells of the Sydney Opera House resemble sails.
Their sweeping, white forms were designed to echo the sails of yachts moving across Sydney Harbour. This visual connection helps the building appear rooted in its waterfront setting rather than looking like a conventional theatre or concert hall.
Danish architect Jørn Utzon developed the design, whose expressionist geometry evolved into curved forms derived from sections of a sphere. The exterior is often called a group of “sails,” while architects and engineers more precisely describe the underlying structures as concrete shells.
A common mix-up is to call them waves because of the building’s harbour location and undulating outline. Waves describe the surrounding setting, but “sails” is the standard answer for what the roof forms resemble. The shells were completed using thousands of prefabricated concrete sections and covered with a distinctive ceramic-tile pattern.