This empire is known by the name of the kingdom of prester-john.
c.1300, Prestre Johan, legendary medieval Christian king and priest, said to have ruled either in the Far East or Ethiopia. From Vulgar Latin *prester, a transition between Latin presbyter and English priest. First mentioned in the West by mid-12c. chronicler Otto of Freising, who told how Johannes Presbyter won a great victory over the Persians and the Medes. Between 1165 and 1177 a forged letter purporting to be from him circulated in Europe. All this recalls the time when the Christian West was culturally backwards and militarily threatened, dreaming of a mythical deliverer. Cf. Old French prestre Jehan (13c.), Italian prete Gianni.