Besides the city wall, other famous Ming-era structures in the city included the famous Ming Xiaoling Mausoleum and Porcelain Tower, although the latter was destroyed by the Taipings in the 19th century either in order to prevent a hostile faction from using it to observe and shell the city or from superstitious fear of its geomantic properties.
One possibility the Tower was destroyed was to prevent it's use by a hostile enemy. What is the other possibility?
superstitious fear of its geomantic properties