Zhangjiawan City Wall Ruins, the starting point of the Beijing-Hangzhou Grand Canal.

Located in Zhangjiawan Town, Tongzhou District, the Zhangjiawan City Wall Ruins were built in the 43rd year of the Jiajing period of the Ming Dynasty (1564). The existing city wall is the southern gate of Zhangjiawan City and the eastern section of the city wall ruins, with a total length of 120 meters. In 1992, the Tongzhou County People's Government allocated funds for repairs and restored 20 meters of the western end according to the original appearance of the Ming City. The restored section is 7 meters high and 35 meters thick, with brick walls, battlements, rammed earth, square bricks on top, and the lower half using old bricks from the original city and lime grouting. The remaining 80 meters retain the original appearance, with a height of 4 meters. There is also a 50-meter city foundation at the east wall, turning north to the Tonghui River. The ancient town has many historical relics, such as the Tongyun Bridge, which was built in the Liao Dynasty and rebuilt as a stone bridge during the Wanli period of the Ming Dynasty. It spans the Xiaotaihou River, with a length of 43.5 meters, a width of 10 meters, and a three-hole stone arch structure. The stone lions on the bridge have different postures. With a long history and rich cultural heritage, Zhangjiawan was named in the 22nd year of the Zhiyuan period. It has witnessed the changes of the times from a bustling dock to the sub-center of Beijing. In addition, it is said that Cao Xueqin's residence was located here, and the prototype of Lin Daiyu entering the Jia Mansion in "Dream of the Red Chamber" is also related to it.