永定河
Paper money was first issued in Beijing during the Jin. The Lugou Bridge, over the Yongding River southwest of the city, was built in 1189. Seventeen Jin emperors are buried in Fangshan District, including those whose tombs were originally built in Shangjing and moved to Zhongdu. The city's population grew from 82,000 in 1125 to 400,000 in 1207 (and from 340,000 in the surrounding region to 1.6 million).