Did medieval scholars believe the Earth was round?

In classical philosophy I read that around 350 BC, Aristotle declared that the Earth was a sphere and about a century later Aristarchus and Eratosthenes measured the size of the Earth. Although much of the ancient Greek's writings were destroyed by the Church during the dark ages Aristotle's work was preserved.

People knew the Earth was round since the Greeks, around 200 BC. In 240 BC, Eratosthenes, thou even as far back as 500 BC. Eratosthenes measured the angle of a shadow cast by a stick he had planted in the ground, at exact noon on the summer solstice in Alexandria, Egypt. Unlike other region called Syene, he measure that cast NO shadow; he made an angle of about 7.2 degrees, or about 1/50 of a complete circle. Using the distance of Syene and Alexandria, he could get 50x and calculate the circumference of the Earth.

Gerbert d'Aurilla (c.946 – 1003) reintroduced the concept of a spherical earth to Western Europe. He taught and promoted the use of armillary spheres. Granted his version had the earth as the center of the "universe" as opposed to the sun. (And of course the sun is the center of the solar system and not the center of the universe.)

Gerbert later became pope (Sylvester II) and further promoted the armillary sphere.

We can say that as of the turn of the millennium (1000 AD) it was understood, in educated circles, that the earth was a sphere.

In God's Philosophers: How the Medieval World Laid the Foundations of Modern Science, James Hannam states that:

The myth that a flat earth was part of Christian doctrine in the Middle Ages appears to have originated with Sir Francis Bacon (1561–1626), who wrongly claimed that geographers had been put on trial for impiety after asserting the contrary. There were a few authentic flat-earthers in late antiquity, but none among the scholars of the Middle Ages proper.

Even scholars from the very early medieval period believed the earth to be a sphere. Much has been said on western scholars in other answers (although John Philoponus, died circa. 570 AD, is also worth a mention), but it is also worth looking at India and Aryabhata (476 to 550 AD). This mathematician and astronomer's work influenced Persian and Arabian scholars and he calculated the circumference of the earth with only a very small error:

Modern estimates suggest that Aryabhata’s computation was 39,968km (24,835 miles), just off the currently accepted value of 40,074km by an incredible 0.27%.

This diagram explains how he probably did it. In his commentary GolapAda, Boogola or Gola, Aryabhata

applied plane trigonometry to spherical geometry by projecting points and lines on the surface of a sphere onto appropriate planes. Topics include prediction of solar and lunar eclipses and an explicit statement that the apparent westward motion of the stars is due to the spherical Earth’s rotation about its axis. Aryabhata also correctly ascribed the luminosity of the Moon and planets to reflected sunlight.

According to the article Spherical Shape of Earth as described by Aryabhata I, he wrote that

The globe of the Earth stands...in space at the centre of the circular frame of the asterisms...surrounded by the orbits (of the planets); it is made up of water, earth, fire and air and is spherical...

I have a tiny bit of evidence of another type to add about medieval belief in a spherical Earth.

A globus cruciger is a globe or orb topped by a cross, and part of the regalia of Christian monarchs.

In ancient times gods and monarchs were depicted with orbs that symbolized the spherical Earth and/or the spherical heavens believed to surround the Earth.

After Constantine I converted to Christianity the Christian emperors began to be depicted holding globes with crosses on top to symbolize that Christianity would someday rule the world.

https://en.wikipedia.org/wiki/Globus_cruciger1

https://www.google.com/search?q=globus+cruciger&newwindow=1&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjd4obC6Y_bAhXrg1QKHTbvAqQQ_AUICygC&biw=1904&bih=9302

I once read that for an imperial coronation in the 11th century, possibly that of Conrad II or Henry III, a hollow imperial orb was filled with dirt from the different realms ruled by the emperor, thus showing that in that specific case the orb was definitely believed to represent the spherical Earth and not the spherical heavens.

I believe that I read that in a book by Edward Francis Twining, Baron Twining, either A History of the Crown Jewels of Europe (1960) or European Regalia (1967).

Medieval Scholars were much more sophisticated than they are usually given credit for.

Knowledge of the shape of the Earth were never really "lost". Apart from their own observations, there were also classical works that supported this view. During late antiquity, Boethius had access to Ptolemy, even if it later was forgotten and had to be reintroduced to Western Europe. Two other works, however, Pliny's Natural history and Platon's Timaeus were available throughout the period. There are a few examples of scholars that suggested other shapes, but they were exceptions, not the rule.

Some examples

Adam of Bremen (second half of eleventh century) is known as a historian, and an important source of Nordic history, but in his Gesta Hammaburgensis Ecclesiae Pontificum he also wrote on the midnight sun:

[In the north], you can during summer, at the solstice, see the sun above the horizon for fourteen days in a row, and during winter it disappears in the corresponding manner for as many days. This is strange and bewildering for the savage peoples, as they do not know that the shifting length of the days is a consequence of the higher or lower orbit of the Sun. From the spherical shape of the Earth, it follows necessarily, that when the Sun closes in, brings daylight, but as it removes itself leaves night. When it rises during the solstice, it prolongs the days and shortens the nights for those who lives in the north, but when it sets during the winter solstice, it does the same for those in the south.

It appears that he got this from Bede's The reckoning of time, but it does show that the knowledge was well spread.

Vincent of Beauvais (c. 1184/1194 – c. 1264) correctly described what would happen if an object was dropped in a hole through the entire world.

Nicole Oresme (c. 1320–1325 – 1382) correctly argued that there were no way of knowing if it was the Earth that rotated, or the celestial sphere; if the air and water moved with the Earth, there would be no physical sensation. He did in the end say that he believed in a stationary Earth, but that seems more a matter of tradition.

Sources

I translated the passage from Adam from the Swedish of Emanuel Svenberg's translation.

Vincent of Beauvais I found mentioned in C.S. Lewis The Discarded Image.

Nicole Oresme is quoted at length in Károly Simonyi's A cultural history of physics. It also contains a useful introduction to what classical works were available to medieval scholars.

You can see De sphaera mundi by the astronomer Johannes de Sacrobosco (c. 1195 – c. 1256) :

"it was one of the most influential works of pre-Copernican astronomy in Europe. Though principally about the universe, De sphaera contains a clear description of the Earth as a sphere which agrees with widespread opinion in Europe during the higher Middle Ages, in contrast to statements of some 19th- and 20th-century historians that medieval scholars thought the Earth was flat."

See the English translation :

THE EARTH A SPHERE. -- That the earth, too, is round is shown thus. The signs and stars do not rise and set the same for all men everywhere but rise and set sooner for those in the east than for those in the west; and of this there is no other cause than the bulge of the earth. Moreover, celestial phenomena evidence that they rise sooner for Orientals than for westerners. For one and the same eclipse of the moon which appears to us in the first hour of the night appears to Orientals about the third hour of the night, which proves that they had night and sunset before we did, of which setting the bulge of the earth is the cause.

For its success, see here :

Johannes de Sacrobosco's 13th century Tractatus de Sphaera was one of the most popular astronomical books of all times. Before the invention of the press, it was widely used in manuscript form. In the 15th century, shortly after the development of printing, it was one of the first scientific books to be published, in 1472. Afterwards, it underwent successive editions – more than 200, up to the 17th century.

Note

Middle Ages lasted from the 5th to the 15th century.

Some dates :

• Bede the Venerable : 672/3 – 26 May 735

• Gerbert of Aurillac (Pope Sylvester II) : c.946 – 12 May 1003

• Johannes de Sacrobosco : c.1195 – c.1256.

The turning point was the contact with the Islamic civilization of Al-Andalus that under the Caliphate of Córdoba from 929 to 1031 became one of the leading cultural and economic centres throughout the Mediterranean Basin, Europe, and the Islamic world.

The rediscovery of Ancient Greek science and philosophy started in Wetern Europe with transaltions from Arabic : the Italian Gerard of Cremona (c.1114 – 1187) went to Toledo (no later than 1144), in the Caliphate of Cordoba, to learn Arabic.

Gerard of Cremona's Latin translation of the Arabic version of Ptolemy’s Almagest made c.1175 was the most widely known in Western Europe before the Renaissance.

In total, Gerard of Cremona translated 87 books from the Arabic language, including such originally Greek works as Archimedes' On the Measurement of the Circle, Aristotle's On the Heavens, and Euclid's Elements of Geometry.

Well, it isn't exactly true that medieval scholars understood the world to be round. They were much, much more subtle in their thinking that that. You see, it was quite clear that the world couldn't be precisely round, and much of their thinking went into improving that model.

To see why the medieval view was much more subtle than authors like Lyon even seem to imagine, you have to understand that the roundness of the Earth was intimately tied to the medieval understanding of the workings of gravity. Of course, in this era no one was close to anticipating anything like Newtonian gravitation. Indeed, they would have considered ridiculous the idea that two bodies could act on each other without some physical connection. (Note: Newton's theory was not broadly accepted as a physical model for decades after publication for the same reason. Newton barely even tried to explain how gravity actually worked. Newton's math, of course, was accepted and celebrated, but scientists struggled for years to come up with a mechanism that allowed for what appeared to be "action at a distance".)

Instead of Newtonian gravity, the Aristotelian thought common in the Middle Ages held that objects rose or fell according to their elements in a kind of sorting process, all things tending to the center of the universe (that is, Earth). Objects made of Earth had the strongest affinity for the center, followed by water, then air, then fire. Thus the Universe is more-or-less a set of concentric spheres, with Earth at the center, surrounded by Water, then Air, then Fire. And every substance naturally seeks it's proper level. This model is quite sensible - most of our everyday observations of rocks, water, bubbles and such seem to confirm it, and what few counterexamples exist can be explained away more-or-less convincingly.

(You might notice that Copernicus' solar-centric model contradicts this model, and Copernicus failed to provide even a cursory explanation of how his system could work. Putting a fiery body at the center of the system quite literally turns the universe upside-down. Copernicus' math may have been excellent, but lacking a theory of gravity, his physics were absurd.)

So medieval scholars not only understood the world to be round, they had a fully developed physical theory of gravity which demanded that the world was round. Lyon could not have been more wrong - the roundness of the Earth was central to the entire understanding of how the Universe worked. But scholars knew that there was a problem with this entire worldview - indeed, the problem was right beneath their feet.

The riddle they struggled with was simple: how can there be dry land? The general expectation was that there were similar (if not exactly the same) amounts of earth, air, fire and water in the universe. But if there were similar amounts of earth and water, and the earth was (almost) entirely closer to the center than the water, then the water layer should be very thick and there should be not a bit of dry land poking above this layer. Scholars provided many different theories to explain this, all of which required some deviation from the simplistic statement that the world was round. They considered the possibility that the water-sphere had a different center than the earth-sphere, that the earth-sphere was egg-shaped, and other alternatives. The one explanation that seems to have completely eluded them is that there isn't nearly as much water as earth, and that the water just forms a thin shell on the surface. This theory quietly became universal within a few decades of Columbus' discoveries, almost without debate.

In sum, medieval scholars weren't all ignorant rubes that thought the world was round. They knew the world was much more complicated than that!

Thomas Aquinas wrote a number of works in the 13th century, some of which were introductory (at least to medieval students - less so to today's students, who are not familiar with scholastic terminology). Most of these would have been read by many, if not most, scholars during their Trivium studies.

One of these works, well-known to this day, is the Summa Theologica.

In the very first Quaestio, specifically in Iª q. 1 a. 1 ad 2, Thomas discusses the different ways of arriving at truth. As an example (!), he notes that astronomers (astrologus in medieval nomenclature) and natural philosophers demonstrate that the earth is round (rotundus) by mathematical arguments and by recourse to matter itself.

Ad secundum dicendum quod diversa ratio cognoscibilis diversitatem scientiarum inducit. Eandem enim conclusionem demonstrat astrologus et naturalis, puta quod terra est rotunda, sed astrologus per medium mathematicum, idest a materia abstractum; naturalis autem per medium circa materiam consideratum.

Here is a translation:

Sciences are differentiated according to the various means through which knowledge is obtained. For the astronomer and the physicist both may prove the same conclusion: that the earth, for instance, is round: the astronomer by means of mathematics (i.e. abstracting from matter), but the physicist by means of matter itself.

Thus, the roundness of the earth was apparently accepted generally enough that it did not require further demonstration or argument but could be used as a throwaway example to illustrate a more fundamental issue.

Edit: Ctrl-C takes issue with rotundus possibly meaning "round" rather than "spherical". Fair enough. Happily, Thomas Aquinas also wrote the Summa Contra Gentiles, and in lib. 2 cap. 38 n. 9, again as an illustration that requires no further argument, says:

... sicut simul dum sol est in puncto orientis, illuminat nostrum hemisphaerium.

It does not get much more (hemi-)spherical than hemisphaerium.