The Classical Period also saw an increase in the use of statues and sculptures as decorations of buildings. The characteristic temples of the Classical era, such as the Parthenon in Athens, and the Temple of Zeus at Olympia, used relief sculpture for decorative friezes, and sculpture in the round to fill the triangular fields of the pediments. The difficult aesthetic and technical challenge stimulated much in the way of sculptural innovation. Most of these works survive only in fragments, for example the Parthenon Marbles, roughly half of which are in the British Museum.