What is "gubeikou"

Gubeikou is a town of Miyun County in northeastern Beijing, bordering with Luanping County, Hebei to the north and the Beijing towns of Gaoling to the west, Xinchengzi to the east and Taishitun . The area is one of the important passes of the Great Wall of China, serving as an ancient chokepoint for travelers between the Northeast and Beijing. , it had 4 residential communities and 9 villages under its administration.