Prester John’s castle (299) bulks large in the interior of Africa. In the twelfth century, reports spread through Europe of the vast realm of a fabulous Christian monarch in the heart of Asia. By the fourteenth century, however, Prester John’s empire had been transferred to Africa, where it became associated with the Christian kingdom of Abyssinia. The elaborate edifice with which Leardo represents Prester John’s empire may be intended for the sumptuous palace described in the thirteenth-century _Letter of Prester John_. Like most medieval cartographers, Leardo makes the Nile (312) rise in West Africa (338). In this he follows Herodotus, Pliny, Mela, and other ancient authorities. Ptolemy, however, seems to have had a more correct view, placing the sources of the river in the Mountains of the Moon in eastern Africa. Nothing daunted, most of the fifteenth-century cartographers who used the writings of Ptolemy boldly transferred the Mountains of the Moon to West Africa to suit their theory of the river’s course. Thus, on the Leardo map we see the Montes Lunae (334) on the north coast of the West African gulf. Thence four streams flow north into a lake, out of which the Nile makes its way eastward and another stream flows westward into the Atlantic. The latter stream represents, perhaps, a combination of Niger and Senegal, of which some faint knowledge may have been gained through traders who had crossed the Sahara. The lower Nile is joined by the River “Stapus” (313), doubtless the Astapus of Ptolemy or the modern Blue Nile. On the Este map this tributary rises in the Terrestrial Paradise, there placed in East Africa. To the mountain range of North Africa, the Carena of the Catalan maps, Leardo has added Ptolemaic names (385-392). The Mediterranean The outlines of the Mediterranean (433) and Black Seas (431) are more correct than any other features which Leardo draws. This, of course, is due to the fact that they were derived ultimately from the portolan charts. Leardo preserves the faulty orientation of the Mediterranean characteristic of the latter. If we assume that the perpendicular line extending from the wind-blower off the west coast of Spain through Jerusalem to the wind-blower east of the Terrestrial Paradise is intended to run due east and west, we see that the axis of the Mediterranean with the adjoining shores has been turned counter-clockwise some twelve degrees. This is probably because of failure on the part of the makers of the original portolan charts to take into consideration the declination of the compass.[24]