The Forbidden City was built with a sophisticated flood-resistant drainage system. The terrain of Beijing is higher in the northwest and gradually slopes downward toward the southeast. The design of the Forbidden City follows this natural topography, with the northern part elevated and gradually sloping downward to the south, allowing water to drain from north to south into the Golden Water River and the Tongzi Moat. Additionally, the Forbidden City features dragon head spouts that function as drainage outlets. There are as many as 1,142 dragon heads used for water drainage, with a high concentration in key areas such as the Outer Court (including the Hall of Supreme Harmony) and the Inner Court.