Cosmas Indicopleustes was a 6th-century merchant from Alexandria who sailed the Red Sea and Indian Ocean trade routes — his epithet Indicopleustes means "the India-sailor" — and likely became a monk later in life, associated with the Church of the East. His one surviving work, the Christian Topography (c. 550), is illustrated with diagrams and world maps that are among the oldest surviving maps from the Christian world and some of the earliest examples of Christian manuscript illustration; because the surviving Greek manuscripts are thought to copy his own originals, he is effectively one of the earliest map-makers whose work we can still see. Those illustrations are prized by historians not only as cartography but as a visual record of his travels — he drew and described the lands, peoples, plants, and animals he encountered, including some of the earliest Western depictions of creatures like the rhinoceros and giraffe.
In the Christian Topography, Cosmas argued that the universe was shaped like the biblical Tabernacle — a flat, rectangular Earth beneath a vaulted lid, with mountains tall enough to hide the sun and cause night. Drawing on the literal scriptural method of the School of Antioch, he wrote it explicitly to oppose the "pagan" Greek doctrine of a spherical Earth. It is also important to note that Cosmas had essentially no followers; his work was ignored throughout the Middle Ages.
Cosmas had been to the edges of the world the philosophers only theorized about — felt the Red Sea heave under a real hull, copied a real inscription off a real stone at Adulis with his own hand. What had Aristotle done but reason from a chair? Cosmas had crossed those horizons himself and come back to draw what he saw.
That was what he could not forgive — not that they disagreed, but that so few had looked, mocking a world they had never tested, citing a sphere they had met only in someone else's book. So he did the one thing an honest man could do against borrowed certainty: he documented. Page after page of lands and peoples, the rhinoceros and the giraffe, the routes and the tides — evidence stacked like timber, so no one could wave him away as a fool with an opinion.