Imagine how the world appeared to the ancient Greeks and Romans: there were no aerial photographs (or photographs of any sort), maps were limited and inaccurate, and travel was only by foot, beast of burden, or ship. Traveling more than a few miles from home meant entering an unfamiliar and perhaps dangerous world. Celestial bodies could provide orientation to the north and south, but there was no way to determine east and west except by dead reckoning. Yet despite this, Greeks, beginning in the sixth century BCE, were able to travel far and wide, and by the third century BCE had determined the size and shape of the earth, using nothing but mathematics and simple tools.
It is probable that the enclosed nature of the Mediterranean assisted in early exploration, since its coasts could be explored relatively easily, something that was done by the sixth century BCE. Sailors were also the first to determine an essential nature of the earth: that its surface was not flat but curved, obvious from the sinking of coasts below the horizon as one left port. Eventually Greek seamen left the Mediterranean and explored down the West African coast, north into the Arctic, and determined the route from the Red Sea to India. Overland travel was more difficult, but central Europe, sub-Saharan Africa, and parts of southern Asia were known by the Roman period. All things considered, it was amazing that Greeks and Romans traveled as far as they did. Although there was no sense of “exploration” (in the modern sense) in antiquity, those who needed to travel—traders, merchants, and military and political personnel—were able to collect a vast amount of data about the surface of the earth and its peoples.
Greeks, beginning in the sixth century BCE, were able to travel far and wide, and by the third century BCE had determined the size and shape of the earth, using nothing but mathematics and simple tools.
Yet scholars wondered about other things: what was the actual size and shape of the earth? How much of it had actually been covered? These were issues more scientific than a matter of exploration. Since sailors had determined that the earth was curved, it eventually fell to Pythagorean theorists to theorize it must be a sphere: how else could its curvature, visible in all directions when at sea, be explained? This was one of the most remarkable leaps of imagination from classical antiquity, almost totally counter-intuitive, but nonetheless correct. By the fourth century BCE Aristole pointed out that if one sailed west from the entrance to the Mediterranean (at the ancient Pillars of Herakles, the modern Straits of Gibraltar), one would eventually reach India, a concept of great interest to Renaissance explorers such as Columbus.
But how big was the earth? Just how far was it west from the Pillars to India? In another amazing feat of ancient scholarship, Eratosthenes of Kyrene in the second half of the third century BCE was actually able to determine this, aided by two simple circumstances. Simple observation had determined that at Syene (the first cataract of the Nile) the sun was directly overhead at the summer solstice, and no shadows were cast. From Syene the Nile flowed due north to its mouth at the great city of Alexandria, where, on the summer solstice, the sun was still somewhat in the south, creating shadows whose angle could be determined. Using a measuring stick, called a gnomon, it was possible to create a great triangle from Alexandria to the sun (based on the angle of the shadow), and back to Syene, where (since there were no shadows) a right angle existed. Since the distance from Syene to Alexandria had been carefully measured, and two angles of the triangle were known, it was possible to determine what portion of the earth’s circumference was represented by the angle at Alexandria. This is a simplified summary of Eratosthenes’ technique, which enabled him to calculate that the circumference of the earth was 252,000 stadia, remarkably close to the accurate figure.
Eratosthenes also invented the word “geography,” and using his techniques, it was now possible to create a grid system and plot the location of almost any point on the surface of the earth. Krates of Mallos, in the second century BCE, created the first globe of the earth. But it was soon realized that the earth was immense in its size and that despite the extensive travels of Greeks (and eventually Romans) to what seemed to be the ends of the earth, the known world was only a small part of the earth: Syene was far to the south, but still well north of the equator, and the farthest north Greek settlements, on the north shore of the Black Sea, were only halfway to the North Pole. Yet further exploration of the southern hemisphere and whatever existed west of the Pillars of Herakles was left to Renaissance explorers. But one cannot diminish the importance of Eratosthenes’ feat, using nothing but his eyes, some realities of geography, and a measuring stick.
An essential part of classical scholarship is the evidence that survives today and which enables modern readers to learn about the world of antiquity. Eratosthenes’ actual treatises, his Geography and Measurement of the Earth, are long lost. But we are lucky to have surviving an amazing work, another Geography, written by Strabo of Amaseia and completed during the first two decades of the first century CE. It is one of the most lengthy works surviving from Greek antiquity, and has within it almost everything that has been described previously in this summary, and much more. It is through Strabo that we learn about Pythagorean theories on geography, Eratosthenes, Krates’ globe, Syene, and Greek explorers to the ends of the earth. The Geography of Strabo can be a difficult read, but it itself is a truly amazing work that reveals the astonishing feats of ancient geographers.
Featured image credit: By MagentaGreen, translated by Deu (File:Eratosthenes world map). CC BY-SA 3.0 via Wikimedia Commons.