Beijing, also known as Peking and meaning Northern Capital, is located at the north end of the North China Plain. It has a metropolitan population of 11.9 million. Important building complexes are the old imperial cluster called the Forbidden City, and the new communist government cluster called Zhongnanhai. Between them is Tianamen Square. Other notable buildings are the China World Trade Center twin towers with a third forthcoming 330 meter one, and the Graeco-Roman-style Auditorium of Tsinghua University.