Cross over the Youngding River, the Lugou Bridge, 20 km southwest of the urban city, is the most ancient existing multi-arched stone bridge in Beijing. The construction of the original bridge on this site commenced in the Dading 29 of Jin Dynasty (1189) and ended in the Mingchang 3 of Emperor Zhangzong of Jin (1192). The bridge is 266.5 m in length and 9.3 m in width with 11 arched culverts. There are altogether 281 stone carved balusters on both sides of the bridge. On top of the balusters, 501 stone lions are carved, big or small, all vividly portrayed in different shapes. As early as 700 years ago, Marco Polo, the Italian explorer who travelled throughout China, wrote in The Travels of Marco Polo that the Lugou Bridge is "a unique, and the best bridge in the world'： As the bridge is known to Europeans because of Marco Polo's book, it is also called the "Marco Polo Bridge'： On July 7,1937, the imperial Japanese army launched a full-scale war of aggression against China in Lugou Bridge, which was called the "Lugou Bridge Incident" (also known as the "Double-Seven Incident") in history. It marks as the the first shot of Chinese anti-Japanese army in the all-round resistance against Japanese aggression.