Yarkand
From Tardis Wiki, the free Doctor Who reference
Yarkand was a small town (PROSE: Marco Polo) on the western side of Cathay, near the Kashgar Valley. The Old Silk Road began in Yarkand.
The First Doctor, Susan, Barbara, and Ian travelled through Yarkand with Marco Polo and his caravan, while moving from the Plain of Pamir to the town of Lop. (TV: "The Roof of the World") While in Yarkand, the caravan traded oxen for horsees. (PROSE: Marco Polo)
Behind the scenes
Yarkand is never seen in the story itself, as Marco Polo's narration bridges the gap of the journey from the Plain of Pamir to Lop. This narration, however, describes the journey through Yarkand in scarce detail.