Tianjin is located in the northeast of the North China Plain, facing the Bohai Sea in the east and lying between 38°33'-40°15' N, and 116°42'-118°03'E. It adjoins Beijing in the north and borders on Hebei in the east, west and south, covering an area of 11,305 sq km. Its coastal line stretches about 133 km long. Its name first appeared in the early years of the Yongle reign of the Ming Dynasty, meaning the ferry port used by an emperor. In 1404, it became a military position of strategic importance, and construction of city walls and garrison installations began. The city was eventually called Tianjin Fort.