or lowered, and have 40 to 60 cabins for the merchants and only one tiller. They can navigate without a compass, because they have an astrologer, who stands on the side and, with an astrolabe in hand, gives orders to the navigator". (Text from the Fra Mauro map, 09-P25.) Fra Mauro explained that he obtained the information from "a trustworthy source", who traveled with the expedition, possibly the Venetian explorer Niccolò de' Conti, who happened to be in Calicut, India, at the time the expedition left: "What is more, I have spoken with a person worthy of trust, who says that he sailed in an Indian ship caught in the fury of a tempest for 40 days out in the Sea of India, beyond the Cape of Soffala and the Green Islands towards west-southwest; and according to the astrologers who act as their guides, they had advanced almost 2,000 miles. Thus one can believe and confirm what is said by both these and those, and that they had therefore sailed 4,000 miles". Fra Mauro also comments that the account of the expedition, together with the relation by Strabo of the travels of Eudoxus of Cyzicus from Arabia to Gibraltar through the southern ocean in antiquity, led him to believe that the Indian Ocean was not a closed sea and that Africa could be circumnavigated by her southern end (Text from Fra Mauro map, 11, G2). This knowledge, together with the map depiction of the African continent, probably encouraged the Portuguese to intensify their ultimately successful effort to round the tip of Africa. Americas Other than Greenland, the Americas were unknown to Europeans in 1450. Greenland is included in the map as a reference to Grolanda. Circumference of the Earth As was generally the case among medieval scholars, Fra Mauro regarded the world as a sphere. However, he used the convention of describing the continents surrounded by water within the shape of a disc. In one of the texts, the map includes an estimate of the circumference of the earth: "Likewise I have found various opinions regarding this circumference, but it is not possible to verify them. It is said to be 22,500 or 24,000 miglia or more, or less according to various considerations and opinions, but they are not of much authenticity, since they have not been tested." Miglia is Italian for miles, a unit that was invented by the