From the Tang poet Wang Wei's
送元二使安西 (also titled
渭城曲 or
阳关三叠): the friend, Yuan Er, was being sent on a mission to the Anxi Protectorate (near modern Kuqa, Xinjiang).
阳关 (Yang Pass) lay southwest of Dunhuang in Gansu; in ancient times, to pass it was to leave the central plains behind. Set to music, the poem became
阳关三叠, the most famous of all farewell songs.