Guyaju ruins are a group of houses carved out of rock. The ruins are known as the largest site of Northern China showing ancient cave dwellings. They located in the village Dongmenying, near the city of Zhangshanying, in Yanqing County, north of Beijing municipality. The structure carved into the rock has been worked by a 1000 year old community that has left few historical traces. Archaeologists believe that the site dates back to the last period of the Tang Dynasty and the beginning of the Liao Dinasty. The work is attributed to a Mongolic steppe tribe called Kumo Xi. When the Tang dynasty collapsed the Xi rose in rebellion in 847, and were subsequently and disastrously defeated by Zhang Zhongwu. The Xi disbanded and they were betrayed and absorbed by the Khitan people and they eventually established the Liao Dynasty in 907. However, it is believed that when this tribe was on the run, they built here their home and they lived here for 30 years. The ruins look like a fortress in a canyon.
The site is composed by 117 caves and more than 350 rooms and halls, scattered along the northern, southern and eastern slopes. Most of the caves has three rooms, with a small living room and a warehouse. Some homes are two-storey and they are connected by carved stairs, stone bridges and steps. Every room has its defined purpose: communal events, royal quarters, religious rituals, cooking, storage, livestock, living, etc. It has its own drainage and water storage system.
Rooms are of different shapes and size: rectangular, round or square, the largest is 20 meters long, while the smaller 3 meters. Average room height is 1.6/1.7 meters, the tallest 1.8 m. For this reason scholars assume the community that resided there could not exceed 1.4/1.5 meters in height. Archaeologists have speculated that the proportions of the space may indicate that the houses had been built for a community of people of small stature. In the literature there are no documents of this curious place. However there is a reference to a family named Xi living in the northeast of China; the family was later betrayed and for this reason the clan moved to the area, which is now known as the County of Yanqing. They lived in the mountains, but we don't know the exact location. Some speculate the reason for their run forced them to secrecy and to build their own fortified settlement in a hidden mountain. The story of this family reminds the later history of the Kumo Xi, for this reason it's possible the Xi family was the Kumo Xi people on the run. There are other speculations about the origin of this site: some says it was built during Tang Dynasty and it was large granary built and funded by the government. Others think it was a garrison built during the Han Dyansty.
This site is still an enigma as we don't have enough historical evidence to tell the origins of this archeological site.