In a detailed cartouche on the map, Fra Mauro (active ca. 1430-ca. 1459/1464) explicitly references early Portuguese navigation along the African coasts. He notifies readers that Portuguese ships had sailed over 2000 miles, proceeding south-southeast as far as the southern meridian of Tunis. He acknowledges that he had gathered this information from Portuguese maps, thus providing the earliest testimony of Portuguese cartography.
Among Fra Mauro’s sources was a nautical chart designed in London by his fellow Venetian and collaborator Andrea Bianco (active ca. 1430-ca. 1464), who provided numerous place names as far as “Cabo rosso”, near the equator, where, he claimed, “the northern pole could not be seen”. The representation of lands south of the Sinus Ethyopicus, although conjectural, clearly assert the possibility of navigating beyond the torrid zone as far as the southern point of Ethiopia Australe.
By combining Portuguese navigations with accounts of the voyages of Chinese junks which had traveled over 2000 miles in the early 15th century to reach the southern coasts of Ethiopia, Fra Mauro concluded that it was possible to circumnavigate Africa. This intuition anticipated by almost a half-century the voyages of Bartolomeu Dias (ca. 1450-1500), who reached the Cape of Good Hope in 1488.