 In 1550, having once more been refused a request for trade, Altan Khan invaded the Xuan–Da region.However, despite several attempts, he could not take Xuanfu due to Weng Wanda's double fortified line while the garrison at Datong bribed him to not attack there.Instead of continuing to operate in the area, he circled around Weng Wanda's wall to the relatively lightly defended Gubeikou, northeast of Beijing.