Great Wall of China

The Great Wall of Cathay, (TV: Marco Polo) or the Great Wall of China, (PROSE: Childhood Living, COMIC: In-Fez-Station) lay along the course of the Yellow River. According to the First Doctor, it was twenty feet wide. (PROSE: Childhood Living) According to Ian Chesterton it was 2000 miles long. (PROSE: Marco Polo)

Geography
The ancient cities of Su-Chow and Kan-Chow, as well as Lan-Chow and the town of Sinju, were located along or near the Great Wall. (TV: "The Wall of Lies")

History
Marco Polo claimed the wall was built 300 years before the birth of Jesus Christ. Tegana claimed it was built to keep Tartars and War Lords. like him, out of Cathay. (PROSE: Marco Polo)

In 1289, Marco Polo's caravan travelled along the Great Wall for many miles. (TV: "The Wall of Lies") Barbara was the first to spot it, almost calling it the "Great Wall of Chi-" before correcting herself with "Cathay". (PROSE: Marco Polo)

The Tenth Doctor and Donna Noble visited the site of the Great Wall of China during the Qin dynasty, as it was still being built. (COMIC: The Immortal Emperor)

In 1904, Yasmin Khan, Dan Lewis and Eustacius Jericho, who were stuck in 1900s after being sent back in time by the Weeping Angels, left a large message near the Great Wall to attract Karvanista's attention. (TV: Survivors of the Flux)

Before 2005, the Ninth Doctor visited the Great Wall of China and was photographed doing so. Clive Finch later showed this image to Rose Tyler. (PROSE: Rose)

In China, Harry's grandfather was once arrested, with his boyfriend, for attempting to steal a section of the Great Wall. (TV: Knock Knock)

In 2021, Karvanista noted the message, left by Yaz, Dan and Professor Jericho over a century ago, but couldn't do anything about it, since he didn't have time travel. (TV: Survivors of the Flux)