Flat Earth: The World in the Middle Ages #4

An imaginary depiction of Biruni
Location: Museum of the History of the Peoples of Uzbekistan - Tashkent

The Middle Ages and the Earth

The worldview of the Middle Ages was quite different from our modern scientific perception; it was defined by a cosmic model where aesthetic and religious elements were intertwined. The Middle Ages was a period in world history when religion had a profound influence on human life. While educated people sought truth through research on the Earth using scientific methods, the majority of society’s views were shaped by religious explanations. As a result, conceptions of the Earth varied across different regions due to differing religious and cultural traditions. By the end of the Middle Ages, the idea of free thought began to spread under the influence of the Renaissance. This development paved the way for the Scientific Revolution of the 16th and 17th centuries. Ultimately, ideas about the Earth transformed into scientific concepts shaped by experiment and observation; thus, traditional, theological, and symbolic worldviews began to lose their significance. During this process, many ideas about the Earth were presented to the public with supporting evidence, becoming part of the body of knowledge.

The Earth in Medieval Europe

Throughout the Middle Ages, educated circles (especially churchmen, university scholars, and aristocrats) knew that the Earth was spherical. This knowledge had been inherited from Ancient Greece (particularly Aristotle and Ptolemy) and was transmitted as a core part of scholastic education. According to the Ptolemaic cosmos, the heavens consisted of transparent crystal spheres. Each planet was “attached” to these spheres and moved by intelligences—rational beings appointed by God. The Earth stood at the center (the geocentric model), followed by the Moon, Mercury, Venus, the Sun, Mars, Jupiter, Saturn, the fixed stars, and finally the Primum Mobile (the prime moving sphere). Beyond these spheres lay the Empyrean—the realm of divine light where God resided.

The heavens were also believed to hold moral meaning; each planet and star was thought to possess a character (for example, Mars was associated with war, Venus with love). The universe was finite in size, yet in terms of its sacred order and meaning, it presented a wholeness beyond human comprehension. The concept of a vacuum was rejected; every place had its “natural” substance and position. The universe was orderly and imbued with meaning; the principle of “value according to place” was valid: what was high was considered sublime and divine, while what was low was deemed earthly and material.

Regarding continents and oceans, it was believed that the Ocean was an endless ring of water surrounding the Earth. In the outer ocean lived giant creatures, monsters, and unknown races. According to established knowledge, there were three continents: Europe, Asia, and Africa. Yet some maps also depicted an imaginary southern landmass (terra incognita). Although pilgrimages, the Crusades, and merchants’ travels (such as those of Marco Polo) brought new information, nautical knowledge remained limited.

Within Europe, there were also small regional variations in worldview. In the lands of the Holy Roman Empire, mystical tendencies accompanied scholastic thought due to more abstract cosmologies developed by thinkers like Nicolaus Cusanus. In France and England, the influence of Thomas Aquinas was strong. Aristotelian cosmology was powerful at universities like Paris and Oxford. In Spain, both Muslim scientific heritage and Christian thought played a role. The Toledo translations deepened Europe’s scientific understanding of the cosmos.

The Earth in the Islamic World of the Middle Ages

In the medieval Islamic world, views about the Earth and the universe were influenced by both the Qur’an and Ancient Greek science (especially Aristotle and Ptolemy). During the Abbasid period, a great translation movement began, especially in Baghdad; Greek philosophy and natural sciences were translated into Arabic and developed by Muslim thinkers. This influence is clearly visible in the works of al-Farabi, the founder of Islamic philosophy. His cosmology bore strong Neoplatonic and Aristotelian influences. According to him, the Earth was spherical and stood motionless at the center of the universe. The cosmos consisted of nested spheres revolving around the Earth. Al-Farabi argued that the movements of celestial bodies were perfectly circular. In his model, the Sun, like the other planets, orbited the Earth within its own sphere.

One of the Islamic scholars who came after al-Farabi, al-Biruni, had a more empirical and observation-based approach to the Earth. He continued to defend the Earth’s spherical nature, supporting it with mathematical evidence. Al-Biruni imagined a massive triangle with one corner at the top of a mountain, another at the Earth’s center, and the third at the horizon. Using the mountain’s height and the angle between the mountaintop and the horizon, he calculated the Earth’s radius. By this method, he measured it as 6,340 km (3,940 mi). Today we know the Earth’s equatorial radius is 6,378 km (3,963 mi) and its polar radius 6,357 km (3,950 mi). Considering that al-Biruni lived in the 10th–11th centuries, this was a remarkable achievement. He also discussed the idea that the Earth rotates on its own axis, but could not prove it; therefore, his official position was that the Earth was motionless. In his work al-Qanun al-Mas’udi, he even discussed the possibility that the Earth might orbit the Sun and that the Sun, not the Earth, might be the center of the universe, though he could not find sufficient evidence for this claim.

In the 13th century, Nasir al-Din al-Tusi introduced the famous “Tusi couple,” a mathematical device showing linear motion as the combination of two circular motions. With this model, he solved some of the problems in Ptolemy’s system. He accepted that the Sun orbited the Earth but introduced innovations in the mathematical explanation of its movement. His work produced more complex but more accurate models of celestial motions.

In the 14th century, Ibn al-Shatir developed innovative astronomical models. To resolve flaws in Ptolemy’s planetary models, he used new mathematical systems, such as refined epicycle models, to describe planetary motion more accurately. Interestingly, Ibn al-Shatir’s models later showed similarities to those of Copernicus.

In summary, the general view in the Islamic world was that the Earth was spherical. Especially toward the end of the Middle Ages, astronomical studies were mostly based on the geocentric (Earth-centered) model, and the prevailing belief was that this model was correct. However, scholars such as Abu Sa’id al-Sijzi, al-Biruni, Ibn Yunus, and Ibn al-Haytham also explored heliocentric (Sun-centered) models. Due to observational limitations, the complexity of the Ptolemaic system—which still predicted celestial motions fairly accurately—and religious interpretations consistent with the geocentric model, these attempts did not succeed. Nevertheless, the mathematical tools and observational techniques developed by Islamic scholars later made significant contributions to the works of Copernicus, Kepler, and Galileo, and thus indirectly to the “Astronomical Revolution” in Europe.


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