 Wang Khan, Toghrul of the Keraites, a Nestorian Christian monarch whom Marco Polo identified as the legendary Prester John, is said to have had his palace here (the Black Forest of the Tuul River) and forbade hunting in the holy mountain Bogd Uul.The palace is said to be where Genghis Khan stayed with Yesui Khatun before attacking the Tangut in 1226.Founded in 1639 as a yurt monastery, Ulaanbaatar, originally Örgöö (palace-yurt), was first located at Lake Shireet Tsagaan nuur ( directly east of the imperial capital Karakorum) in what is now Burd sum, Övörkhangai, around south-west from the present site of Ulaanbaatar, and was intended by the Mongol nobles to be the seat of Zanabazar, the first Jebtsundamba Khutughtu.