Mercator's Prester John is depicted by the mapmaker as seated on a royal throne and holding up a cross, symbolizing his dual role as temporal and spiritual leader of his empire. The inscription readers 'Prete Giam magnus imperator Abbissini'... Mercator imagined the kingdom of Prester John as being centered on the upper Nile River, evoking earlier traditions of the mighty priest-king possessing the power to regulate or shut off the flow of the life-giving Nile.