As I showed last Friday, the Ancient Greeks, Romans, and Egyptians knew and accepted as a matter of course that the Earth was spherical. This knowledge was not lost and continued to be accepted as fact throughout the medieval period.
[Modern sculpture of Aryabhata on the grounds of IUCAA Pune, source: Wikimedia Commons]
The Venerable Bede is one of the earliest medieval Europeans we know of to make reference to the Earth as a sphere in the early 8th century. He used this in The Reckoning of Time to explain the unequal length of days as the seasons changed. This work was particularly widely copied and read due to Carolingian requirements for priests and was generally accepted without further proofs. Additionally, the circulation of a few ancient works such as Plato’s Timaeus meant that medieval Europeans knew quite well that the Earth was round.
[Pages from a Latin copy of Plato's Timaeus, early 10th century, source: Wikimedia Commons]
[Image of Ibn Sina on a modern Tajikistani banknote, source: Wikimedia Commons]
These works came to the universities of Christian Europe through Al-Andalus. Western Europeans already knew the Earth was round, but these ancient texts and the commentaries on them and produced both a new interest in the topic. Thomas Aquinas on several occasions used this fact as an example of something already known, which Roger Bacon and others speculated whether or not the equator was too hot to be crossed.****
[Image from the Liber Divinorum Operum, HIldegard von Bingen, 12th century]
[Source: Wikimedia Commons]
The spherical nature of the Earth was not up for debate in this time period. People knew it already. The question of whether the Earth went around the Sun or vice versa, on the other hand was the subject of significant debate, but that is a topic for another time.
*He should technically belong in the Ancient post rather than the Medieval one but I accidentally left him out. So he gets his own paragraph here.
**Names of interest here include Al-Ma’mun (a 9th century Caliph who hired several astronomers and geographers to calculate the distance between to cities as well as the curvature and the circumference of the Earth), Al-Farghani (one of the astronomers hired by Al-Ma’mun), and Abu Rayhan Biruni (an 11th century scholar who developed a more accurate way of calculating the Earth’s circumference).
***Known in Europe as Avicenna and Averroes respectively. Ibn Rushd was so famous in Western Europe as a translator of and commentator on Aristotle that many works refer to him simply as “the Commentator.”
****Christopher Columbus proved that it could. He did not prove that the Earth was round because 1) he and everybody else already knew that and 2) that’s not what he was arguing. He used Al-Farghani’s calculation of the Earth’s circumference in Arabic miles and treated it as though it were in Roman miles to prove (wrongly) that the Earth was much smaller than people said it was.
The Aryabhatiya (Translated by Walter Eugene Clark) - Wilbour-Hall (Note: not searchable, unfortunately)
Aryabhata - Wikipedia
Claudius Ptolemy, Almagest - Central Connecticut State University
Bede the Venerable, De Temporum Ratione - Chronologie und Kalender (Note: This is in Latin. I was unable to find an English translation online.)
The Reckoning of Time - Wikipedia
Bede the Venerable - Wikipedia
Plato, Timaeus - MIT.edu (Search "globe" for the reference.)
Timaeus (dialogue) - Wikipedia
Aristotle, De caelo Part 2 - MIT.edu (Search "spherical" and you'll find the reference.)
Aristotle, Meteorology Part 1 - MIT.edu
Aristotle, Meteorology Part 2 - MIT.edu
Al-Ma'mun - Wikipedia
Al-Farghani - Wikipedia
Abu Rayhan Biruni - Wikipedia
Biruni's Measurement of the Earth - Geogebra
Ibn Sina - Wikipedia
Ibn Rushd - Wikipedia
Averroes - Islamic Philosophy Online (This is a collection of works by Ibn Rushd, mostly in Arabic and English.)
Hildegard of Bingen - Wikipedia
Johannes de Sacrobosco - Wikipedia
Thomas Aquinas, Summa Theologica, Question 1, Article 1 - Christian Classics Ethereal Library
Thomas Aquinas, Summa Theologica, Question 54, Article 2 - Christian Classics Ethereal Library
Thomas Aquinas - Wikipedia
Roger Bacon - Wikipedia
Spherical Earth - Wikipedia