Who First Realised the Earth was Round?

James Hannam

Few questions have given rise to as much confusion as “who discovered that the Earth is round?” Many people still think folk in the Middle Ages thought the world was flat until Christopher Columbus discovered America. In fact, its true shape was well known in medieval Europe. Another widespread error is that Pythagoras was the first to declare that the Earth is round. This is stated on websites belonging to the likes of NASA, the BBC, and the Encyclopaedia Britannica. It’s probably the fault of a certain Sir Thomas Little Heath (1861–1940). The youngest son of a farmer, he owed his knighthood to being permanent secretary at HM Treasury during the First World War, and his fellowships of the Royal Society and British Academy to his studies of ancient mathematics. Even today, his translations of Euclid and other Greek mathematicians are the standard versions in English.

Unfortunately, Heath made a few mistakes. One notable mis-step was to credit the discovery that the Earth is a sphere to Pythagoras (c. 570–c. 500 BC). Heath’s Aristarchus of Samos: The Copernicus of Antiquity (1913 and still in print) begins with a brief history of astronomy up until Aristarchus’ time in the 3^rd century BC. In the section on Pythagoras, we learn that the ancient sage “attributed spherical shape to the Earth for the simple reason that ‘the sphere is the most beautiful of the solid figures’”.^[1]T.H. Heath, Aristarchus of Samos: The Ancient Copernicus (Cambridge UP, 1913) 51. This sounds plausible and is consistent with traditional views about Pythagorean thought. But when we dive into the sources, we can find precious little evidence for it. In fact, today’s experts on Pythagoras conclude that we can’t know anything much about what the man himself might have believed.

As it happens, the earliest extant reference to the Earth being a globe comes from 200 years after Pythagoras was born, in a dialogue by Plato (427–347 BC) called the Phaedo (108e). While Plato didn’t invent the idea, it’s clear from his remarks that it was a novel and inchoate concept at the time. On that basis, we should date the genesis of the spherical earth to the early 4^th century BC. However, the waters have been irremediably muddied by Diogenes Laertius (AD c. 180–240), who wrote Lives of Eminent Philosophers, our main source for much of the lore about Greek philosophers. In this book, he named no less than four early figures, including Pythagoras, as being the first to say that the Earth is round. Words like “unreliable” and “fanciful” are commonly used to describe poor Diogenes, but this isn’t really fair. He was a compiler rather than an editor, whose work consists of a series of anecdotes and factoids gleaned from his reading numerous books, many of them unavailable today. And, helpfully, he often tells us what those books were.

Diogenes noted two different ancient sources that claimed Pythagoras was the first to say the Earth is round. The first reference (8.1.26) comes from a lost book written in the 1^st century BC, called The Succession of Philosophers by Alexander Polyhistor. He was a Greek enslaved by the Romans in the Mithridatic Wars (88–63 BC) and taken to Italy to be a tutor. He eventually gained his freedom and became a Roman citizen. Alexander didn’t have any first-hand evidence about Pythagoras and the globe. His information came from some memoirs written perhaps in the 4^th century BC, so well after the time of Pythagoras himself. Diogenes’ other reference (8.1.49) comes from Favorinus, a Sceptical philosopher active in Rome in the 1^st century AD. We don’t know why he said that Pythagoras thought the Earth to be round, although, by this time, the ancient sage had been credited with all kinds of arcane knowledge and abilities. In short, the evidence for Heath’s contention is very flimsy.

If we don’t fancy the candidature of Pythagoras, Diogenes had a few alternatives. One (8.1.49), a claim attributed to Zeno of Elea (c. 495–430 BC), was the early hexameter poet Hesiod (fl. 7^th century BC). But this is a ridiculous suggestion: Hesiod’s poems clearly assume that the Earth is flat. Diogenes also put forward (2.1.1) the pre-Socratic philosopher Anaximander of Miletus (c. 610–c. 546 BC). The trouble is, we have it on better authority that Anaximander said the Earth was a squat cylinder, like a column drum, held in place at the centre of the universe, and that we live on the flat upper surface (DK 12.A.10–11).^[2]This and other “DK” references are drawn from the 5^th edition of Die Fragmente der Vorsokratiker (3 vols, Berlin, 1934–7), edited by Hermann Diels and Walter Kranz.

The final name suggested by Diogenes (9.21) is Parmenides of Elea (515–450 BC). Here, at last, we might be getting somewhere. Parmenides is famous for concluding that change is an illusion, a doctrine he relayed through the medium of poetry. Quite a few fragments of his poem survive, quoted by later writers, so we can piece together some of his ideas from his own words. The fragments show he believed that the universe is like a ball. This makes sense, since a sphere looks the same from wherever you observe it and is the shape that best exemplifies Parmenides’ doctrine that reality is immutable. Perhaps it would not be surprising if he thought the Earth was round as well.

Diogenes tells us (8.1.49) that he found the information about Parmenides in a work by Theophrastus (c. 371–287 BC), a younger contemporary and close associate of Aristotle. While several of the books of Theophrastus survive, his famed History of Science, from which Diogenes is doubtless quoting, has been lost. Still, we can be confident that Theophrastus himself had access to Parmenides’ original poem, so the information in Diogenes is only second-hand.

Unfortunately, the case against giving the credit to Parmenides is formidable. First, while surviving fragments of his poem do state that the universe is spherical (DK 28.B.8), there is no similar statement about the Earth. Indeed, he seems to have thought the world we can perceive was formed from alternating wreaths of light and darkness, even if the whole is contained within a sphere. (DK 28.A.37) Thus, inside the universe, his cosmology is two-dimensional, consistent with a flat Earth. Furthermore, apart from Diogenes, we have no other source that attributes a spherical Earth to Parmenides.

Theophrastus is usually a reliable source and it seems likely that he did say that Parmenides was the first to state the world is a sphere. However, there is plenty of room for ambiguity. In the fifth century BC, the word Parmenides used that comes closest to “the world” is πᾶν (pān), which means “the whole” or “everything”. However, by the time of Theophrastus, 150 years later, it was much more common for philosophers to use the word κόσμος (kosmos), which had originally meant “order”. When Diogenes was writing, the meaning of kosmos had widened further: it could mean the whole universe, the Earth, or even humanity. The potential for confusion is worsened by the fact Diogenes says Parmenides called the Earth “round” as well as “spherical” – just like we do. However, at the time Parmenides was writing, the Earth was generally assumed to be a disc, which could just as well be described as “round” as a ball can be. Given the uncertainty, it is impossible to be confident about what Parmenides actually meant.

Another celebrated 5^th-century philosopher was Anaxagoras of Clazomenae (c. 500–c. 428 BC). Anaxagoras subscribed to the view that the Earth is a flat disc surrounded by a spherical heaven. Did he also consider whether the Earth might actually be a sphere? There is an intriguing hint that he might have done contained in Plato’s dialogue the Phaedo, which, as we noted above, is also the earliest extant reference to the Earth being round. The dialogue is set in the prison where Socrates (c. 470–399 BC) was awaiting his execution, but written about 30 years later.

Near the start of the conversation, Socrates notes that he had once consulted a book by Anaxagoras. “I assumed,” Socrates says, “that he would begin by informing us whether the Earth is flat or round, and then he’d explain why it had to be that way because that was what was better.” (97d) Many scholars have assumed that this means Anaxagoras really did begin his book with a discussion of the shape of the Earth. However, Plato didn’t actually write this – rather Socrates is made to voice the assumption that Anaxagoras would consider whether the Earth be round or flat, with the implication that in fact he did not. Socrates goes on to say he was prepared to learn about the sun, moon and other heavenly bodies – their relative velocities and orbits. All this reflects the state of Greek astronomy in the 370s, when the Phaedo was composed, rather than nearly a century earlier when Anaxagoras wrote his book. In any case, the philosophical point that Plato was making is that Anaxagoras explained the world using physical causes rather than considering the best way God could have created the universe. The shape of the Earth is incidental.

While it is unlikely that any contemporaries of Anaxagoras were full-blown globalists, the Earth’s form was a matter of debate through the second half of the 5^th century BC. For example, an obscure figure called Archelaus (fl. c. 450 BC) said that the Earth is shaped like a bowl, with a marsh at its lowest point. Life arose from this wetland. As evidence for the depression at the centre of the Earth, he noted that the times the sun rises and sets are not the same for everyone (DK 60.A.4) Unfortunately, this argument doesn’t work, since it would mean the sun would appear first to people living on the western side of the Earth as it rose over the eastern horizon. Those in the east would still be in the shadow of the bowl’s rim until the sun rose a bit higher. This is obviously the opposite of what we observe – dawn comes first to those in the east.^[3]A late alchemical text, The Assembly of the Philosophers, seeks to correct this error by stating that Archelaus thought the Earth was shaped like a hill. See A. Laks and G.W. Most (edd.), Early Greek Philosophy, (Loeb Library, Harvard UP, Cambridge MA, 2016), 7.216.

Dmitri Panchenko has noted that the dispute over whether the Earth is flat or a dish is also referenced by the late-antique Latin writer Martianus Capella (360–428).^[4]Dimitri Panchenko, “Anaxagoras’ Argument Against the Sphericity of the Earth,” Hyperboreus 3 (1997) 175–8. Martianus wrote a Latin textbook on the seven liberal arts called the Marriage of Mercury with Philology. The conceit of the book is that seven erudite young ladies, representing the liberal arts, each give a speech at the nuptial celebrations.

Geometria, the personification of geometry, discusses the shape of the Earth (6.590). She begins by noting that it isn’t a flat disc, as some people imagine, nor does it have a dip in the middle. Rather it is rounded, a sphere even. She dismisses the concave model as not worth anyone’s time. Then she notes that even the great Anaxagoras had thought the Earth was flat. As evidence for this, he explained that when the sun or moon rise above the horizon, their light is immediately directed to our eyes in straight lines. As it stands, this argument makes sense as, if the Earth were flat, everyone on it would see the sun rising at the same time.

Panchenko and the great scholar of the pre-socratics, Daniel Graham, think this passage is evidence that Anaxagoras was arguing with people who believe the earth is spherical.^[5]Daniel W. Graham, Science Before Socrates: Parmenides, Anaxagoras, and the New Astronomy (Oxford UP, 2013) 128. Indeed, that is what Martianus himself was asserting. However, as we’ve seen, in the context of the 5^th century BC when Anaxagoras was active, debates about the shape of the earth featured the theory that it was bowl-shaped, which is a hypothesis that Martianus had actually just talked about. So, if Martianus had somehow managed to tap into some otherwise unknown account of Anaxagoras debating the shape of the Earth, he was probably defending his position that the Earth is flat against someone like Archelaus, who said it was dish-shaped.^[6]Panchenko (as n.4) and Graham (as n.5) both link the argument cited by Martianus to another mentioned by Aristotle, who had said supporters of a flat earth said the horizon appears straight rather than curved when observed against the rising sun (On the Heavens 2.13 294a1). However, the two arguments are very different and it is hard to see how they could have been conflated.

Overall, we lack any reliable references to the Earth being round dating from the 5^th century BC or earlier. There are also some notable silences – places we might expect the subject to be referenced when in fact it is not. For example, when Aristotle discusses the ideas of his predecessors, he often names them. However, when he comes to those who think the world is round, he doesn’t mention anyone. And The Clouds, a play by Aristophanes from 423 BC which satirises the weird ideas of philosophers such as Anaxagoras and Socrates, didn’t refer to the globe. Given how he deliberately mocks cosmological speculation, it’s hard to see how Aristophanes could have resisted poking fun at the absurd concept of a spherical earth if anyone was already talking about it.

All this strongly suggests that no one proposed that the Earth is a sphere until a few decades before Plato noted the idea in the 370s. Thus, the common statement that the Greeks knew the Earth to be round from the 6^th or 5^th centuries BC is unjustified. Perhaps someone had a flash of inspiration some time around 400 BC. It’s frustrating we can’t know who they were.^[7]In my book, I have tentatively suggested Philolaus…

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Dr James Hannam is the author of The Globe: How the Earth became Round (Reaktion, London, 2023) and God’s Philosophers: How the Medieval World Laid the Foundations of Modern Science (Icon, London, 2009). He likes to write about the interactions of science, religion and philosophy, particularly in the ancient and medieval worlds. He can be found at the site formally known as Twitter as @drjameshannam and lives in Kent, England.

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Further Reading

The best guide to early Greek astronomy for general readers, even after all these years, is D.R. Dicks, Early Greek Astronomy to Aristotle (Thames and Hudson, London, 1970).

A more recent and excellent survey (although I don’t always agree with it) is Daniel Graham’s Science Before Socrates: Parmenides, Anaxagoras, and the New Astronomy (Oxford UP, 2013).

My book The Globe: How the Earth became Round (Reaktion, London, 2023) traces the development of the Ancient Greeks’ ideas about the Earth and how the theory that it is a sphere spread around the world. 

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The image at the top of this article is a woodcut from Camille Flammarion’s L’Atmosphere: Météorologie Populaire (Paris, 1888, p.163), which depicts a medieval thinker looking with terror over the edge of the Earth. It has been beautifully coloured by Wiki user Raven.