Polo, with his father and uncle, left for Cathay in the year 1271. By his twenty-fifth birthday in 1277, he had come into the service of Kublai Khan. In 1287, Marco, his father and uncle asked the Khan to be permitted to return home. The Khan refused.
Polo encountered the First Doctor, Ian, Barbara and Susan on the Plain of Pamir in 1289 and promptly seized the TARDIS as a gift for the Khan. He hoped it would be sufficiently impressive to buy his way out of the Khan’s service so he could return home. The Doctor and his companions were forced to make a long overland journey with Polo, during which time They got to know him well. He had prevented an assassination attempt on the Khan’s life by the Mongol warlord Tegana. Following this, Marco returned the TARDIS keys to their owners to allow their escape as Tegana’s body was removed. Barbara claimed that she knew that Polo would see Venice again. (Marco Polo)
In a alternate timeline which may have been invalidated by Big Bang Two, Polo purchased the Pandorica. As always, an Auton reconstruction of Amy Pond’s fiancée, Rory Williams, accompanied the box. (The Big Bang)