The United Nations Headquarters was designed by an international committee of architects chaired by Wallace K. Harrison. It was championed by John D. Rockefeller, Jr., who donated a site initially assembled for real estate purposes by William Zeckendorf. Its 18-acre plot is now an international zone belonging to all Member States. The architectural team included well-known architects Oscar Niemeyer & Le Corbusier, along with representatives of eleven other countries. The narrow slab of the UN's Secretariat Building is 39 stories and only 72 feet thick while rising some 544 feet above plaza base. Overall, the Headquarters consist of 4 main buildings: the General Assembly building, the Conference Building, the Secretariat building, & the Dag Hammarskjold Library, added in 1961. To help link the development with the rest of Manhattan to the west, under the direction of Robert Moses, 1st Ave. traffic was diverted into a tunnel making way for United Nations Plza. above. Similarly, the FDR also passes beneath the conference center building. The complex is currently slated for a major refurbishment designed to upgrade its mechanical systems & environmental characteristics.