This doesn’t mean, as has often been suggested, that there was no medieval astronomy. We need only cite the story of Gerbert d’Aurillac, the tenth-century pope Sylvester II, who in order to obtain a copy of Lucan’s Pharsalia promised an armillary sphere in exchange; not realizing that the Pharsalia had been left incomplete on Lucan’s death, upon receiving an incomplete manuscript he gave only half of the armillary sphere in exchange. This indicates the great attention given to classical culture during the early Middle Ages, but it also indicates the interest in astronomy at the time. Ptolemy’s Almagest and Aristotle’s De caelo were translated during the twelfth and thirteenth centuries. As we all know, astronomy was one of the subjects of the quadrivium taught in medieval schools, and in the eighth century John of Holywood’s Tractatus de sphaera mundi, based on Ptolemy, was to be the undisputed authority for centuries to come.
Yet it is also true that geographical and astronomical notions had long been confused by the ideas of authors such as Pliny or Solinus, for whom astronomy was certainly not of uppermost concern. The picture of the Ptolemaic cosmos, formed perhaps indirectly through other sources, was theologically most credible. Each element of the world, as Aristotle taught, had to remain in its proper natural place, from which it could be moved only by violence and not by nature. The natural place for the earthly element was the center of the world, whereas water and air had to remain in an intermediate position, and fire was at the edge. It was a reasonable and a reassuring picture, and this idea of the universe enabled Dante to imagine his journey into the three realms of the afterlife. And if this representation did not take account of all celestial phenomena, Ptolemy himself contrived to introduce adjustments and corrections, such as the theory of epicycles and deferents, according to which, in order to explain various astronomical phenomena such as accelerations, positions, retrograde motions, and the variations in distances of various planets, it was supposed that each planet rotates around the Earth along a larger circle, called the deferent, but also moves in a small circle, or epicycle, around a point C of its own deferent.
Lastly, the Middle Ages was a period of great travel, but with the roads in disrepair, great forests to pass through, and stretches of sea to be crossed at the mercy of buccaneers, there was no possibility of drawing adequate maps. They were purely indicative, like the instructions in the Pilgrim’s Guide at Santiago de Compostela, which said, more or less, “If you want to get from Rome to Jerusalem, head southward and ask along the way.” Now, try thinking of the rail maps you find with train timetables. No one could deduce the exact shape of Italy from that series of junctions, each perfectly clear in itself when you have to take a train from Milan to Livorno (and realize that you have to change at Genoa). The exact shape of Italy is of no interest to anyone traveling to that station.
The Romans built a series of roads that linked every city in the known world, but this is how those roads were represented in the map known as the Tabula Peutingeriana, named after the man who had rediscovered it in the fifteenth century. The upper part represents Europe, with Africa below, but we are in exactly the same situation as the railway map. From this map we can see the roads, our points of departure and arrival, but have absolutely no idea about the shape of Europe, or the Mediterranean, or Africa—and the Romans certainly had a much clearer notion of geography than this. They were not interested in the shape of the continents, but rather in whether, for example, there was a road that would take them from Marseille to Genoa.
Then again, medieval journeys were imaginary. The Middle Ages produced encyclopedias, Imagines mundi, whose authors tried as far as possible to satisfy the taste for wonder, writing about far-off, inaccessible lands, and these books are all written by people who had never seen the places they are describing—the force of tradition at that time was more important than experience. A map did not seek to represent the form of the Earth but to list cities and peoples along the way.
Once again, symbolic representation was more important than empirical representation. In many maps, the illuminator was most concerned about placing Jerusalem at the center of the Earth, rather than showing how to get there. Yet most maps of that period represent Italy and the Mediterranean fairly accurately.
One last consideration. Medieval maps did not have a scientific purpose but instead responded to the audience’s need for wonder, in rather the same way that popular magazines today show us that flying saucers exist and we are told on television that the pyramids were built by an extraterrestrial civilization. The creators of these maps looked up at the sky with the naked eye to see comets, which the imagination immediately transformed into something that (today) would confirm the existence of UFOs. On many fifteenth- and sixteenth-century maps with a reasonably accurate cartographic layout, mysterious monsters are depicted in the lands where they are supposed to live, and are reproduced on the map in a not entirely mythical fashion.
So let us not be too critical of medieval maps. It is with them that Marco Polo arrived in China, the Crusaders in Jerusalem, and perhaps the Irish or the Vikings in America.
A short aside—is it really true, as legend suggests, that the Vikings reached America? We all know that the real revolution in medieval navigation came with the invention of the stern-mounted hinged rudder. On Greek and Roman ships, as well as those of the Vikings and even those of William the Conqueror who landed on the English coast in 1066, the rudder consisted of two rear side-oars, operated in such a way as to set the intended direction of the boat. The system, apart from being fairly exhausting to use, made it practically impossible to maneuver large wooden vessels. Above all, it was impossible to sail against the wind; to do so, it was necessary to tack—to move the rudder so that each side of the boat faced alternately into the wind, first one side and then the other. Sailors therefore had to limit themselves to navigating close to shore, following the coastlines so that they could take shelter when the wind was unfavorable.
The Vikings (and the same was true for the Irish monks) could never, therefore, have sailed from Spain to Central America, as Columbus would later do. But the picture changes if we imagine they first took a route from Iceland to Greenland, and from there to the Canadian coast. Looking at a map, we can easily see how skilled mariners in longships could succeed (with who knows how many shipwrecks along the way) in reaching the far north of the American continent and perhaps the coast of Labrador.
THE SHAPE OF THE SKY
But let us leave the Earth and look at the sky. Aristarchus of Samos had advanced a heliocentric theory between the fourth and third centuries B.C.E., as Copernicus recorded. Plutarch tells us that Aristarchus was accused of impiety precisely because he had put the Earth in movement so as to explain, through earthly rotation, astronomical phenomena that could not otherwise be accounted for. Plutarch did not agree with this theory and Ptolemy later judged it “ridiculous.” Aristarchus was way ahead of his time, and perhaps he reached his conclusion for the wrong reasons. There again, the history of astronomy is curious. A great materialist such as Epicurus developed an idea that survived for so long that it was still being discussed by Gassendi in the seventeenth century, as well as appearing in Lucretius’s De rerum natura. He suggested that the sun, the moon, and the stars (for many very serious reasons) can be neither larger nor smaller than how they appear to our senses. So Epicurus judged the sun to have a diameter of about thirty centimeters.