The first offices in the newly built United Nations Secretariat Building in Manhattan were occupied as UN staff began moving from their temporary headquarters at Lake Success, Long Island. The event became significant not only in the history of the United Nations but also in the evolution of modern real estate, urban development and high rise office architecture.

The 39-storey Secretariat Building rises about 544 feet above street level. Excavation for the UN Headquarters complex began in September 1948, while erection of the Secretariat Building's steel structure started in April 1949. Within a few years, the tower became one of the most recognisable features of Manhattan's skyline.

The real estate story behind the project was equally significant. Before the United Nations established its headquarters there, the East River site was a run down district occupied by slaughterhouses, a railroad garage and other commercial buildings. An $8.5 million contribution from John D. Rockefeller Jr. played a crucial role in securing the site, while New York City later contributed additional property.

The Secretariat Building also introduced a striking architectural language to New York. According to the United Nations, it was the city's first skyscraper to feature all glass curtain walls. Its white and green glass exterior stood in sharp contrast to the brick and stone towers that dominated Manhattan at the time. The design helped popularise a style that would later become standard for corporate office towers around the world.

The project therefore represented far more than the construction of an international institution. It transformed a former industrial waterfront into one of the world's most important diplomatic addresses and demonstrated how a landmark development could reshape the identity and value of an urban district.

August 21, 1950 consequently stands as an important date in real estate history, linking urban regeneration, landmark architecture and the emergence of the modern glass office skyscraper.