Analysis of information sources in references of the Wikipedia article "Beiting Protectorate" in English language version.
上元元年，河西軍鎮多為吐蕃所陷。有舊將李元忠守北庭，郭昕守安西府，二鎮與沙陀、回鶻相依，吐蕃久攻之不下。In the first year of the Shangyuan era [760], the Hexi Army Defense Command fell to the Tibetans. Beiting and Anxi were guarded by Li Yuanzhong and the old general Guo Xin, who along with the Shatuo and Uyghurs, were able to prevent the Tibetans from taking the two garrisons.
建中元年，元忠、昕遣使間道奏事，德宗嘉之，以元忠為北庭都護，昕為安西都護。In the first year of the Jianzhong era [780], Yuanzhong and Xin dispatched envoys through a remote path to memorialize the emperor. Dezong commended them and Yuanzhong became protector-general of Beiting while Xin became protector-general of Anxi.
