Inner City corner guard towers
There are four corner guard towers located at the four vertices of Beijing's inner city walls. They are all similarly designed, multi-eaved Xieshanding style having grey tiles with green glazed edges, its cross-section is curvy zig-zag shaped. The tower alone has a height of 17 metres, adding the height of the platform, its height is around 29 metres to the ground. the two adjacent sides facing out of the city are 35 metres in width respectively, each having four floors fitted with arrow windows, with 14 arrow windows on each floor. The two adjacent sides facing into the city also have four floors fitted with arrow windows respectively, but with only four arrow windows on each floor. These two sides facing into the city also have big openings square in shape with reinforced wooden windows serving as true windows that are normally open for air and light to pass through, while those on the sides facing out of the city are normally closed, and only opened when shooting arrows or cannonballs. The interior of the towers are hollow with no floor board, there are only floor boards immediately hugging the four sides of the towers and connected to the stairs.
Of the four corner guard towers of Beijing's inner city, only the southeastern one survived intact, this was due to its proximity to Beijing's main train station located also in the southeast, when the metro was built, it was thought that building the metro so close to the train station would disrupt the important railroad services into the capital city, and thus a new metro route around the north of the train station was used, therefore sparing the dismantlement of the southeastern corner guard tower and the sections of the inner city walls surrounding the corner guard tower. Of the other three corner guard towers, the northeastern one was dismantled in 1920, and its platform later in 1953; The northwestern corner guard tower was destroyed by Russian cannonfire in 1900 during the Boxer Rebellion, its platform was dismantled later in 1969; The southwestern corner guard tower was dismantled in 1930 because there weren't enough funds for its periodic repair, its platform was dismantled in 1969.