Officially named Zhengyangmen, it is popularly called Qianmen (前门) (front gate) because it is located directly in the center of the southern wall of the inner city of Beijing, which was built around the Forbidden City and the Imperial City in 1420 (the 18th year of the reign period of Emperor Yongle of the Ming Dynasty. One of the nine gates stood along the 20-km inner city wall, it is situated directly in front of the Imperial City and the Forbidden City. The gate-tower was built in 1437 on top of the brick city wall. It is a two-story structure with a traditional double-eave roof. The roof is of hip-and-gable style.