After 14 years of construction the Sydney Opera House, which has been called the most celebrated, vilified, and expensive of all buildings in the world, is complete. Joern Utzon's design was chosen in 1956 from among 223 entries in Sydney's design contest. Although the Utzon drawings were only schematic the judges agreed on the genius of the basic idea, which was that each of the roofs of the major buildings, shaped like ballooning sails, would provide the towering space for a theater within. Two major theaters, one slightly larger than the other, were to be accommodated. The Sydney construction firm of H. R. Hornibrook obtained the main contract in 1961. When the formwork got under way the list of contractors on the tall billboard at the front entrance showed that they came form Denmark, England, France, Germany, Italy, and the United States. The arches, which are post-tensioned, were precast in segments of beam arches, ridge beams, slabs and tile panels. Fifteen foot ribs of five to 13 segments each were cast on the site to support the shells. These segments were set one above another on each side of each shell until they met at the apex. A top ridge beam segment was then placed as a keystone. Rib sections were temporarily post-tensioned together during construction and permanent cables were installed later. Stressing cables were also run through the tops of adjacent ribs and through the keystone to tie the structure together.