The state of Qin fortified the Hangu Pass to the east of Tongguan as its eastern border and it continued to protect the Chinese heartland from outside attack during the Qin and Han dynasties. During the Eastern Han that succeeded Wang Mang's short-lived "Xin dynasty", the guards at Hangu reversed themselves and protected Luoyang in the plains from attacks coming from the west.
During both the Qin and Han dynasties, the state of Qin fortified Hangu Pass to its east as a defensive border against external threats. In the Eastern Han period that followed Wang Mang's brief "Xin dynasty", the guards at Hangu shifted their focus and protected Luoyang in the plains from western invasions.