Su-Chow

Su-Chow was an ancient city in Cathay, south-west of Tun-Huang. It was found near the beginning of the western side of the Great Wall of Cathay and was located near Kan-Chow. (TV: "The Wall of Lies") A way station was located there. (PROSE: Marco Polo)

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. (TV: "The Wall of Lies") They did not stay in the city long, however, only ever camping near the city, with Marco insisting they not stop until they reach Kan-Chow. (PROSE: Marco Polo)

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. It is described in the novelisation, however, but only from afar as the travellers journey past the city.
Su-Chow (modern spelling Suzhou) is now known as Jiuquan in the real world.