Su-Chow

 was an ancient city in Cathay, south-west of Tun-Huang. It marked the beginning of the western side of the Great Wall of Cathay and was located near Kan-Chow.

In 1289, the First Doctor, Susan, Barbara, and Ian visited Su-Chow, after leaving Tun-Huang with Marco Polo on their journey to the court of Kublai Khan. Their next stop would be in Kan-Chow. (TV: "The Wall of Lies")

Behind the scenes

 * The journey through Su-Chow was only mentioned in Marco Polo's narration. As such, Su-Chow is never actually seen in the serial itself.
 * Su-Chow (modern spelling Suzhou) is now known as in the real world.