In Renaissance cathedrals, domes tended to replace the Spires of medieval churches. Since ancient times, large public buildings such as these have required special materials and organization of labour, timber frames and clay bricks supported houses, but monuments required stone blocks and large gangs of Labor to move them. Bricks and stone blocks form the basic building material of most European and American architecture until the modern era. Modern buildings, however, use strong steel and reinforced concrete. Girders covered in glass and plastic. Powerful machines enable the large scale construction of 20th century office towers. Ice scrapers have become the dominant structures in the centre of most cities in the world. Exciting new architectural designs have made use of radical new materials and experimental visual styling. Churches, art galleries and performing arts halls provide the architect with an opportunity to stretch creative powers. They have often become landmarks of particular cities, as the famous Opera House has become a distinctive emblem of Sydney, Australia. The ground area surrounding buildings is often designed, especially by landscape architects, parks, water fountains and sculpture gardens provide restful and visually interesting. Areas within the city core. Since the decline of interest in modernist towers, many traditional styles of design from around the world have been brought together in the architecture of post modernism. Architects working in this style are calling for a more human scale of building and trying to make structures stylistically appropriate to the surrounding community. Like the visual art world in the 1980s, there is no single dominant style of architecture. Contemporary architects are free to stretch their imaginations in any direction.