Subsequent demonstrations of the Earth’s roundness, though, were based on empirical observations. Ptolemy, of course, knew that Earth was round; otherwise he wouldn’t have been able to divide it into 360 degrees of longitude. But Parmenides, Eudoxus, Plato, Aristotle, Euclid, and Archimedes had already understood this. And Eratosthenes knew it in the third century B.C.E., when he had calculated fairly accurately the length of Earth’s meridian, calculating the different inclination of the sun, at midday on the summer solstice, when it reflected into the bottom of the wells of Alexandria and Syene (now Aswan). But—so far as the Earth being flat—I must digress for a moment to say that there is not only a history of imaginary astronomy, but also an imaginary history of astronomy, which still survives today in many scientific circles, not to mention in popular opinion. Try an experiment. Ask any reasonably intelligent person what Christopher Columbus wanted to demonstrate when he decided to reach the East by way of the West, and what the learned men of Salamanca persistently denied. The answer, in most cases, will be that Columbus thought the Earth was round, while the learned men of Salamanca believed it was flat and that after a short distance the three caravels would fall off the edge into the cosmic abyss.
Nineteenth-century secular thought, irritated by the fact that the church had not accepted the heliocentric theory of the universe, attributed to Christian thought (both patristic and scholastic) the idea that the Earth was flat. This idea gained force during the campaign by supporters of Darwin against all forms of fundamentalism. They wanted to show that since the church was wrong about the Earth’s being round, it could be wrong about the origin of species. They therefore took advantage of the fact that the fourth-century Christian writer Lactantius (in his Divinae institutiones) had contested the pagan theories about the roundness of the Earth by arguing that the Bible describes the universe on the model of the tabernacle. It must therefore be rectangular in form, not least because Lactantius could not accept the existence of the Antipodes, where people would have to walk around upside-down.
Then it was discovered that a sixth-century Byzantine geographer, Cosmas Indicopleustes, in his Topografia Christiana, thinking once more of the biblical tabernacle, had claimed the cosmos was rectangular, with an arch over the flat floor of the Earth.
The curved vault remained hidden from our eyes by the stereoma, in other words, by the veil of the firmament. Beneath this was the ecumene, namely, all the land on which we live, which sits on the ocean and slopes imperceptibly and continually upward to the northwest. Here there is a mountain so high that it is lost to our view and its peak disappears among the clouds. The sun, moved by angels—who also control earthquakes, and the rains and all other atmospheric phenomena—passes in the morning from the east toward the meridian, in front of the mountain, lighting up the world, and in the evening it reaches the west and disappears behind the mountain. The reverse cycle is followed by the moon and by the stars.
Cosmas also shows us the Earth as if we were looking at it from above. There is the frame of the ocean, beyond which are the lands where Noah lived before the flood. Farthest east from these lands, separated from the ocean by regions inhabited by monstrous beings, is the earthly paradise. The Euphrates, Tigris, and Ganges spring from paradise. They pass under the ocean and flow out into the Persian Gulf. The Nile takes a more tortuous route via the antediluvian lands, it enters the ocean, continues its course into the low northern regions—more accurately, into the land of Egypt—and flows out into the Golfo Romaico, the Hellespont.
As Jeffrey Burton Russell has shown in his Inventing the Flat Earth (1991), many influential books on the history of astronomy still studied at school claim that Cosmas’s theory became the prevailing view throughout the Middle Ages. They also claim the medieval church taught that the Earth was a flat disc, with Jerusalem at the center, and that the works of Ptolemy remained unknown throughout the Middle Ages. The fact is, Cosmas’s text—written in Greek, a language the medieval Christian had forgotten—became known in the Western world only in 1706 and was published in English in 1897. No medieval writer knew of it.
A first-year pupil at a secondary school can easily work out that if Dante enters the funnel of hell and leaves from the other side, seeing unknown stars from the slopes of Mount Purgatory, this means he knew perfectly well that the Earth was round. But Origen, Saint Ambrose, Albertus the Great, Thomas Aquinas, Roger Bacon, and John of Holywood (to mention just a few) were all of the same view. The point of dispute at the time of Columbus was that the calculations made by the learned men of Salamanca were more accurate than his. They claimed that the Earth, which was certainly round, was larger than our Genoese voyager imagined, and it was therefore pure folly to try to circumnavigate it. Columbus, however, a fine navigator but a useless astronomer, thought the Earth was smaller than it was. Neither he nor the learned men of Salamanca, of course, suspected the existence of another continent between Europe and Asia. Though they were right, the doctors of Salamanca were wrong; and Columbus, though wrong, faithfully pursued his error and was right—through serendipity.
How did the idea develop that in the Middle Ages people thought the Earth was a flat disc? In the seventh century, Isidore of Seville (though hardly a model of scientific accuracy) calculated the equator to be eighty thousand rods long. Therefore, he thought the Earth was round. But among Isidore’s manuscripts is a diagram that influenced many representations of our planet, the so-called T-O map.
The upper part represents Asia—at the top because, according to legend, earthly paradise was to be found in Asia. The horizontal bar represents the Black Sea on one side and the Nile on the other, and the vertical bar is the Mediterranean, so that the quarter circle on the left represents Europe and that on the right, Africa. All around it is the great circle of the ocean.
The impression that the Earth was seen as a circle is given by the maps illustrating the Commentary on the Apocalypse by Beatus of Liébana. This text, written in the eighth century but illustrated by Mozarabic illuminators in later centuries, was to have a major influence on the art of the Romanesque abbeys and Gothic cathedrals—and its model is to be found in countless other illuminated manuscripts.
How was it possible for people who thought the Earth was round to draw maps showing it to be flat? The first explanation is that we do the same ourselves. Criticizing the flatness of these maps would be like criticizing the flatness of our modern-day atlas. It was a naive and conventional form of cartographic projection.
It could be pointed out that over the same centuries the Arabs had produced more accurate maps, though they had the bad habit of representing north at the bottom and south at the top. But we have to bear in mind other considerations. The first is suggested by Saint Augustine, who was well aware of the debate begun by Lactantius about the cosmos in the shape of a tabernacle, but was at the same time aware of the views of the ancients on the roundness of the globe. Augustine’s conclusion is that we should not place too much emphasis on the biblical description of the tabernacle because, as we know, the holy scriptures often speak through metaphor, and perhaps the Earth is round. But since knowledge about whether it is spherical or not doesn’t help us to save our souls, we can ignore the question.