John of Verona
Jacopo da Verona
Quidam dicuntur Nubiani, nigri de provincia Nubie, sunt Ethiopie, conversi a sancto Matheo sub regno presbyteri Johannis, qui habet Gyon, unum de quator fluminibus paradisi, de alveo suo et habet potestatem auferendi soldano et eciam Nillum fluvium, et ideo soldanus multum timet eum, quia ille fluvius irrigat totam Egyptum.
(There are people, who are said to be the Nubians, who are the blacks of the country of Nubia and are Ethiopians who were converted by Saint Matthew to Christianity under the reign of Prester John. It possesses Gyon, one of the four rivers of paradise, and which has the power to nourish the Sudan and also the river of the Nile, which is the reason why Egypt is in fear because the river rises across Egypt.)
Monumenta Cartographica Africae et Aegypti. Tome IV.II, ed. Y. Kamel (Leiden: 1937).