Harold Lamb 
The Three Palladins 

THE THREE PALLADINS is a novel of Temujin, who became the Great Khan, and his palladins – his warrior heroes – in a day of the sword. Here are high adventures that move across the mysterious and mighty Asiatic continent. The palladins are led to fabled Tangut, land of fertile fields, blue lakes, and the black walls of the castle of the magician, Prester John of Asia.