The United Nations Secretariat Building, or the United Nations Headquarters, is a typical complex in New York City, located in the Turtle Bay neighborhood and stretching along the East River from 42nd to 48th streets, on the east side of Manhattan. The Secretariat is the most prominent building among the United Nations Organization (first assembly in 1946) building complex on an 18-acre site. It is an international zone belonging to all member states. The international-style complex includes four major buildings - the Secretariat, the General Assembly building, the Conference building, and the Dag Hammarskjöld Library. The largest of these is the 39-story Secretariat building - home of the UN's administration. This 550-foot tall structure has become a worldwide symbol of the United Nations. Adjacent to this building is the 5-story General Assembly building. It has a seating capacity of 1,800, where all member nations of the United Nations meet. The conference building behind the Secretariat and General Assembly buildings houses the Security Council, and the Economic and Social Council. The complex is also notable for its gardens and outdoor sculptures. Since its completion in 1953, this building has been serving as the United Nations' headquarters. The actual design for the building was carried out by an international team of 11 architects led by Wallace K. Harrison, Oscar Niemeyer and Le Corbusier. The proposed site for the construction of the building was purchased by John D. Rockefeller Jr. for $8.5 million and donated to the international community in December 1945. The construction works started in 1948. Each level of the construction progressed in the subsequent years and by 1953 the whole complex was ready. This modern complex helped regenerate New York City at the end of the World War II. The east and west facades of the building were furnished with blue-green-toned Thermopane windows. The curtain wall and the spandrels between the window rows of the floors are of glass, only painted black on the inside surface. The windowless north and south ends of the Secretariat are clad in marble plates from Vermont. At the top is a high aluminium grille to conceal the equipment on the roof. The bronze sculpture “Single Form” (1962-63), by Barbara Hepworth, stands outside the Secretariat. The complex is open to the public, with guided tours provided. Tours of the United Nations building offer a wide range of information on both the history and day-to-day running of the UN. The highlights on the building include the 12-foot high by 15-foot wide Chagall Stained Glass window at the east side of the public lobby, the Foucault Pendulum in the general assembly lobby, and artifacts from the nuclear holocaust of Hiroshima and Nagasaki. Adjacent to the United Nations complex is a small public park bordering the East River.