Rubruquis the Franciscan, who in 1253 was sent on a mission into Tartary, was the first to let in a little light on the fable. He writes, "The Catai dwelt beyond certain mountains across which I wandered, and in a plain in the midst of the mountains lived once an important Nestorian shepherd, who ruled over the Nestorian people, called Nayman. When Coir-Khan died, the Nestorian people raised this man to be king, and called him King Johannes, and related of him ten times as much as the truth. The Nestorians thereabouts have this way with them, that about nothing they make a great fuss, and thus they have got it noised abroad that Sartach, Mangu-Khan, and Ken-Khan were Christians, simply because they treated Christians well, and showed them more honor than other people. Yet, in fact, they were not Christians at all. And in like manner the story got about that there was a great King John. However, I traversed his pastures, and no one knew anything about him, except a few Nestorians. In his pastures lives Ken-Khan, at whose court was Brother Andrew, whom I met on my way back. This Johannes had a brother, a famous shepherd, named Unc, who lived three weeks' journey beyond the mountains of Caracatais." This Unk-Khan was a real individual; he lost his life in the year 1203. Kuschhik, prince of the Nayman, and follower of Kor-Khan, fell in 1218. Marco Polo, the Venetian traveller (1254-1324), identifies Unk-Khan with Prester John; he says, "I will now tell you of the deeds of the Tartars, how they gained the mastery, and spread over the whole earth. The Tartars dwelt between Georgia and Bargu, where there is a vast plain and level country, on which are neither cities nor forts, but capital pasturage and water. They had no chief of their own, but paid to Prester Johannes tribute. Of the greatness of this Prester Johannes, who was properly called Un-Khan, the whole world spake; the Tartars gave him one of every ten head of cattle. When Prester John noticed that they were increasing, he feared them, and planned how he could injure them. He determined therefore to scatter them, and he sent barons to do this. But the Tartars guessed what Prester John purposed ... and they went away into the wide wastes of the North, where they might be beyond his reach." He then goes on to relate how Tschengis-(Jenghiz-)Khan became the head of the Tartars, and how he fought against Prester John, and, after a desperate fight, overcame and slew him.