Eratosthenes of Cyrene — Mapping the Hellenistic World (2024)

Towards the end of the 4th century BCE the all-conquering and monolithic Empire of Persia would come crashing down. Despite its defeat at the hands of the Greek cities in the previous century, Persia stood strong at the head of the world, until a King of a once obscure kingdom came storming out of the west, sweeping all before him. This article is the fifth in a series, parts one, two, three and four set some context, but you do not need to have read them first to follow this one.

The conquests of Alexander the great would usher in the Hellenistic age, opening the core territories of antiquity to the new frontiers of the west and expanding horizons to the east. The city that still bears the conquerors name, which he ordered constructed at the mouth of the Nile, would become a microcosm of this age. The library built and patronised by the Ptolemaic Kings in Alexandria would become the centre of scholarship in the known world, and one of its finest minds, amongst many achievements, would be hailed as the father of geography, like Hecataeus of Miletus two centuries before.

Eratosthenes of Cyrene would be the chief librarian of the library of Alexandria throughout most of the 3rd century BCE and tutor to the Ptolemies. His geographic work will be the focus of this article, but first we need to understand the circ*mstances of the world in which he lived.

By the middle of the 3rd Century BCE, the Greek cities had fought themselves to exhaustion. The Athenian Empire had been shattered by the Spartan led Peloponnesian league in 404 BCE after the long drawn out conflict of the Peloponnesian war. The Spartans stepped into Athens’ shoes and attempted to fill the void left by the city’s collapse. A few tumultuous decades of Spartan supremacy followed, which would see the declining power of Sparta unable to hold on to the leadership of the Greek city states, alienating them one by one.

Eventually, with the revival of Athenian fortunes looming, Sparta’s much vaunted hoplite infantry would be defeated on the field at the battle of Leuctra in 371 BCE by the city of Thebes, leading to a decade or so of Theban supremacy. During this time, a hostage held by the city of Thebes would grow up learning statecraft and military tactics from Epaminondas and Pelopidas, the architects of the Theban supremacy. This hostage would go on to become Phillip II of Macedon.

Using what he had learnt, Phillip would turn Macedon from an obscure kingdom into a regional powerhouse, overwhelming the Greek cities and forcing a peace on the exhausted Greek states. Having secured peace in Greece, Phillip would be assassinated before he could carry out his most ambitious plan, an invasion of Persia. However, his son, Alexander, would go on to eclipse his father, carrying the Macedonian banner all the way to India, founding cities and spreading Greek culture as he went.

From 334 BCE, when he invaded Persia, until his death in 323 BCE, Alexander would not only lead armies and conquer great swathes of land, but he would also pursue knowledge and inquiry, testing to the limits the theories about the world which drove Greek thinking. Perhaps the best example for our purposes is his stated desire to reach the ends of the world and the great outer ocean, a desire which would see this Greek king lead an army into India in 326 BCE and realise that the world was a much bigger place than he knew.

Alexander’s conquests would open what was once Persia to the Greeks and other peoples of the west, as well as uniting almost all the territories of antique civilisation under one banner. Creating a melting pot of cultures and a chance to exchange knowledge and increase learning like never before. However, with Alexander’s unexpected death in 323 BCE, his generals would divide his empire between them. The successors, or Diadochi as they became known, would each take the title of king for themselves and Alexander’s vast domain was divided into several successor states, signalling the dawning of what historians would later term the Hellenistic age.

Despite this political division, the breaking of boundaries brought by the conquests remained. Alexander’s once bodyguard and general, Ptolemy, crowned himself king of Egypt in 305 BCE and with it took up the challenge of the construction of Alexandria at the mouth of the Nile. This would become the greatest of the cities which bore Alexander’s name.

Ptolemy would begin the process of turning Alexandria into the beating heart of the Hellenistic world. Not only would it be the place in which Alexander’s body was laid to rest, but also the seat of learning through the famous Royal Library of Alexandria, the greatest library of the Ancient world. The library formed part of a research institute in Alexandria, known as the Alexandrian Mouseion. The Library was planned by Ptolemy I, but probably constructed by his successor Ptolemy II as a place to gather all known knowledge. It was the culmination of the Greek thirst for knowledge which had developed over the preceding centuries. The conquests of Alexander had led to an explosion of knowledge about the world flooding into Greek hands and in Alexandria it would be stored and catalogued.

Under the Ptolemaic kings, intellectuals from all over the Greek world flooded to Alexandria. Estimates vary, but undoubtedly the library held a vast number of books, figures range from 200,000 to 700,000; the library of Alexandria was the internet of its day.

Into this developing environment of intellectual curiosity and accumulation of knowledge under royal patronage would step Eratosthenes in about 245 BCE. Eratosthenes was born in the Greek city of Cyrene on the coast of what is now Libya in 276 BCE. The city had surrendered to Alexander after his conquest of Egypt in 332 BCE and then became a part of the Ptolemaic Kingdom after Ptolemy took control of the region.

In the early 3rd century BCE, the city was flourishing under the Ptolemaic Kings, and Eratosthenes would have benefited from this, having been educated in the traditional Greek way at the local gymnasium. However, he went on to continue his studies by travelling to Athens, the traditional heart of Greek learning.

In Athens, he studied philosophy, learning from various schools including Zeno of Citium, the founder of Stoicism, and at the Platonic Academy. It was probably here, developing from his interest in the work of Plato, that he wrote his first scholarly work entitled the Platonikos, an inquiry into the mathematical foundation of Plato’s philosophy. However, Eratosthenes also developed a wider base of interest, studying poetry as well, writing several works of verse before moving on to write a more sober set of histories, including a work on dating important events beginning with the Trojan war.

These works brought Eratosthenes to the attention of the Ptolemies, with Ptolemy III seeking to bring him as a scholar to the library of Alexandria when Eratosthenes was about thirty. Eratosthenes would accept this invitation and within five years he would become the chief librarian and, as a result, the tutor to the King’s children.

Under the stewardship of Eratosthenes, the library would see a huge programme of expansion, requiring any books which entered the city of Alexandria to be surrendered to the library to be copied to such a high-quality people were unsure whether the returned item was the original or the copy. He also expanded the scope of the library adding sections devoted to the examination of Homer and acquiring many original works of drama. A large amount of this effort was done to fend off the competition from the library of Pergamon, but as a result the library of Alexandria gained a new level of breadth and depth making it the centre of learning and scholarship in the classical world.

It is unfortunate that in later life Eratosthenes contracted ophthalmia, meaning that he became completely blind by the year 195 BCE. Losing his ability to read and observe nature led to an intense depression which resulted in Eratosthenes voluntarily starving himself to death in 194 BCE at the age of 82.

During his time at the Library, Eratosthenes made many contributions to various fields of inquiry, particularly science and mathematics. The breadth of his interest was huge and his achievements in many fields are undeniable. However, he received unfair criticism, being given the nickname ‘Beta’, the second letter of the Greek alphabet because he tried his hand at many things but never achieved the highest accolades in any. The other nickname he acquired, ‘Pentathalos’, for the Olympic athletes who were all-rounders and competed well in many different events, seems a much more apt title.

A friend of Archimedes, he shared a love of mathematics, and devised a simple algorithm known as the Eratosthenes sieve for finding prime numbers. He is also credited with the invention of the armillary sphere, a model of the objects in the sky centred on the earth. He also measured the distance to the sun and moon with a high degree of accuracy, although his estimation of the sun’s diameter was a little off at 27 times that of the earth[1], when in reality it is about 109.

From here, he went on to devise a calendar using his predictions about the ecliptic of the earth in which he stated that there were 365 days in a year and 366 every 4 years, essentially the system we still use today.

For our purposes his most important contributions came in the realm of geography. Using his knowledge of the size of Egypt, Eratosthenes was able to estimate the circumference of the Earth. He knew that the town of Syene was 5,000 stades (800 kilometres) south of Alexandria, and on the same meridian, allowing him to calculate the arc of that meridian. To work out the fraction of the earth his measurement represented, he used a gnomon (a vertical pole set in a public place to measure time), measuring the shadow cast by the gnomon when the sun was at its zenith. This gave him two sides of a triangle, the third side would allow him to calculate the circumference of the earth by being able to observe the angle of the sun’s rays from the top of the gnomon to the edge of the shadow. This produced a figure of 7 degrees 12 minutes, or roughly a 5th of a circle, therefore 5 x 5,000 (his measurement of the meridian arc) gave him a figure of 250,000 stades (46,000 kilometres) for the earth’s circumference. This figure was remarkably accurate, the actual circumference of the earth being a little over 40,000 kilometres.[2] Given the knowledge and tools available to him, this is probably about as accurate a figure as anyone could have hoped for and more recent testing of his theories have proved Eratosthenes method.

From this foundation, he used this knowledge to begin to draw the earth. Using the library of Alexandria for works of reference, Eratosthenes wrote a three-volume work entitled Geography describing and mapping the entire world. Beginning to introduce new concepts such as climate zones and grid lines, these works would later earn him the title, the father of geography. Unfortunately, these writings only survive in fragments and later references, but we can use this information to reconstruct Eratosthenes map of the world.

The map reconstruction can be used alongside what we know of his three-volume work to give us a clear understanding of what Eratosthenes knew of the world, but first let us look at the map itself.

The basic elements common to all maps going back to the Babylonian world map are still present. The world is divided into three continents and encircled by a great outer ocean. However, an increasing amount of detail has been added, bringing the world we are all familiar with almost into being.

The three continents are no longer arbitrarily separated by rivers as with Anaximander, and more detail and nuance has taken hold in the understanding of the continents. The map is in fact less aesthetically pleasing than previous efforts, a reflection of the desire to display the world more as it truly is perhaps.

More detail is added to the shape of the land and continents, demonstrating an increasing understanding of the core territories of the antique world, but on top of this, the lands which were previously displayed as broad strokes and terra incognita are gone and a more detailed understanding of what lay beyond the immediate borders of the classical world is on display. Britain and Ireland being depicted for perhaps the first time, and India slowly beginning to take its familiar shape. These details show that the boundaries of Classical antique civilisation had expanded, and that knowledge of the peripheries was now beginning to flood into its core territories.

Looking closer at the detail, Eratosthenes names over 400 cities and their locations, something that had never been achieved before and again showing that the Classical Antique world was becoming ever more interconnected and knowledge was flowing ever more freely around this melting pot.

Finally, the adding of a grid system shows how geography was beginning to evolve into a more scientific discipline as an effort to apply mathematical practices to the mapping of the earth and standardise its depiction were beginning to be explored. This is further evident when Eratosthenes divided the earth into five climate zones, two freezing zones at the poles, two temperate zones and a zone encompassing the equator and the tropics. This development connects this map to modern designs, giving it an air of familiarity, even if it still shares many characteristics with work stretching back to ancient Babylon.

Turning to what we know of Eratosthenes’ three volume work and placing the map alongside it we can see some more interesting developments.[3]

The first book appears to have been an introduction to the subject and focused on recognising the contribution of his predecessors, but was disapproving of Homer for not providing geographical insight, a significant development in a world which largely believed that the world depicted in the Odyssey was accurate. He also laid out ideas on the origin of the earth, thinking it an immovable globe but with a changing surface. The book also seems to have hypothesised that the Mediterranean was once a vast lake which covered all of the lands surrounding it, only to be connected to the ocean when a passage had been opened in the west sometime in the past.

The second book is where the scientific discipline of geography begins to enter Eratosthenes work. In this section he lays out his method for measuring the circumference of the earth, according to Pliny this is the part of Eratosthenes work where “the world was grasped”.

The final part of the work built a further layer on top of the foundations created in the previous two parts. In what would now be termed a political geography, Eratosthenes described countries and used his grid system to divide the world into sections which he then described. Again, it is unfortunate that the detail of this work is now lost.

In many ways, Eratosthenes’ work represents the culmination of the vast accumulation of knowledge which occurred during the Hellenistic age, and specifically at the library of Alexandria.

Eratosthenes used the access he had to the great collected works stored in the library and the new connections being developed, particularly in the Greek states of the east, to draw together all these threads into a coherent and all-encompassing work, using knowledge of the past and pushing the boundaries of that knowledge further. In the process of this he created a new discipline, that would see the standardisation and development of scientific techniques and theories, which were then used to develop knowledge of the world further still.

The next article will take a step away from map making and turn our eyes to the new boundaries of Antique civilisation in the west, looking at a people whose enterprise and exploration would push knowledge of the world to its limits. We will be turning to the Phoenicians and specifically the city of Carthage.

Main Sources

Robin Lane Fox, “The Classical World; An epic history of Greece and Rome”, Penguin Books, London UK, 2006

Peter Green, “Alexander the Great and the Hellenistic Age”, Orion Publishing Group, London, UK, 2007

Malcolm and Alexander Swanston, “How to draw a map”, Harper Collins Publishers, London, UK, 2019

Brooke-Hitching, Edward “The Golden Atlas: The Greatest Explorations, Quests and Discoveries on Maps”, Simon and Schuster, London, 2018

Brotton, Jerry, “Great Maps: The World’s Masterpieces Explored and Explained”, Penguin Random House, Dorling Kindersley Limited, Great Britain, 2015

[1] Smith, Sir William. “Eratosthenes”, in A Dictionary of Greek and Roman Biography and Mythology. Ann Arbor, Michigan: University of Michigan Library, 2005.

[2] Malcolm and Alexander Swanston, “How to draw a map”, Harper Collins Publishers, London, UK, 2019, Pg21

[3] Eckerman, Chris. Review of (D.W.) Roller ‘Eratosthenes’ Geography. Fragments Collected and Translated, with Commentary and Additional Material. The Classical Review. 2011.