Latest / Timbuktu: Africa's Forgotten Center of Knowledge — Fexingo History / The Timbuktu Scholar Who Calculated the Earth's Circumference
Transcript
- Lucas: Welcome back, Luna. We've talked a lot about Timbuktu's scholars and their libraries, but today I want to focus on one figure who really shows how deep the scientific tradition ran there: Abou Bakr Ibn Ahmad al-Timbukti. Luna: I don't think I've heard that name before. What did he do? Lucas: He was a 15th-century astronomer and mathematician, probably trained at Sankore, and he wrote a manuscript called 'The Gift of the Inquisitive on the Levels of the Spheres.' In it, he described a method for calculating the Earth's circumference that was remarkably accurate—within about 3% of the modern value. Luna: Wait, really? In the 1400s, in Timbuktu? Lucas: Yes. He wasn't working in isolation either. He drew on earlier Islamic astronomers like al-Battani and al-Zarqali, who had refined the methods of Ptolemy. But what's impressive is that Ibn Ahmad didn't just copy them—he made his own observations and calculations, and he taught these methods to his students at Sankore. Lucas: The manuscript itself is a kind of textbook, really. It covers topics in ilm al-falak—that's Islamic astronomy—including how to use an astrolabe, how to determine the qibla direction, and how to calculate the circumference using the angle of the sun at different latitudes. Luna: So he was teaching applied astronomy. Did his students then spread his methods? Lucas: That's exactly what happened. The Sankore curriculum relied on ijazas—teaching licenses—that allowed scholars to certify that a student had mastered a text. Ibn Ahmad's 'Gift of the Inquisitive' became part of that curriculum, and copies of it were made and carried across the Sahel. Lucas: We actually have several surviving copies in the Mamma Haidara Library and the Ahmed Baba Institute. They show marginal notes from later scholars who added their own observations, so it wasn't a dead tradition—it was living science. Luna: That's fascinating. But I've heard some people argue that Timbuktu's scholars were just copyists, not innovators. How do you respond to that? Lucas: It's a persistent myth, and it's rooted in racism more than evidence. If you look at the manuscripts, you see original commentary, corrections to earlier models, and new calculations. Ibn Ahmad's circumference measurement, for example, is not a copy of any known earlier work. It's his own, derived from observations he made at a specific latitude. Lucas: And he wasn't alone. We have manuscripts from other Timbuktu scholars who wrote on algebra, geometry, and medicine. They engaged critically with the Greek and Islamic traditions. The problem is that many manuscripts were lost after the Moroccan invasion of 1591, so we only have fragments. Luna: The Moroccan invasion again. It seems like that was a real turning point for Timbuktu's intellectual life. Lucas: It was devastating. The Saadian sultan Ahmad al-Mansur sent Judar Pasha with arquebusiers, and after the Battle of Tondibi, the invaders sacked Timbuktu. They deported scholars like Ahmad Baba to Marrakesh and looted libraries. Many manuscripts were burned or scattered. Lucas: But here's the thing: some manuscripts survived because families buried them or hid them in trunks. That's how we still have Ibn Ahmad's work. It's a miracle, really. Luna: So what instruments did Ibn Ahmad use to make his observations? Did he have an observatory? Lucas: No permanent observatory, but that was common. Most Islamic astronomers worked with portable instruments. In Timbuktu, they had astrolabes, quadrants, and celestial globes. The astrolabe was particularly important—it's like an analog computer that can measure the altitude of the sun or stars. Lucas: We have records of Timbuktu scholars ordering astrolabes from North Africa, and some even made their own. One manuscript describes how to construct a quadrant from wood and brass, with detailed instructions. Luna: So they were manufacturing scientific instruments locally? That's impressive. Lucas: Absolutely. Timbuktu was a center of craftsmanship as well as scholarship. The same city that produced the mud-brick architecture of Djinguereber also produced finely engraved astrolabes. Lucas: Let me give you a concrete example of Ibn Ahmad's method. He measured the angle of the sun at noon on the summer solstice in Timbuktu. Then he compared that with measurements taken at a different latitude—probably from al-Battani's tables—and used the difference to calculate the circumference. Lucas: His result was about 41,500 kilometers, compared to the modern value of about 40,075. That's an error of only about 3.5%. And remember, he didn't have satellites or GPS. Luna: That's incredible. How does that compare to other pre-modern calculations? Lucas: Eratosthenes in ancient Greece got within 2%, but his method relied on the assumption that Alexandria and Syene were on the same meridian, which they aren't. Ptolemy's calculation was off by about 16%. So Ibn Ahmad's was among the most accurate pre-modern results. Lucas: And he wasn't trying to prove that the Earth is round—that was taken for granted by Islamic scholars, who cited the Quran's description of the Earth as 'spread out' like an egg. The debate was about the exact measurement. Luna: So Islamic astronomy had moved beyond the flat-Earth idea long before Columbus. But Timbuktu was far from the centers of Islamic learning like Cairo or Baghdad. How did they stay connected? Lucas: Through the pilgrimage routes and the trade caravans. Scholars traveled to Mecca, stopping in Cairo and Fez, and brought back manuscripts. They also corresponded with each other. We have letters between Timbuktu scholars and scholars in Egypt and Morocco discussing astronomical problems. Lucas: One of the key texts in the Sankore curriculum was al-Mukhtasar of Khalil—a legal text—but alongside it, they studied works on astronomy. The curriculum was surprisingly broad, covering law, medicine, mathematics, and astronomy. Luna: So a student at Sankore might study law in the morning and astronomy in the afternoon? Lucas: Exactly. And the pedagogy was rigorous. Students had to memorize texts, but also demonstrate understanding through oral exams. The ijaza system ensured that only those who truly mastered a subject could teach it. Lucas: Ibn Ahmad's manuscript includes a section on the use of the celestial globe, which models the stars in three dimensions. Students would learn to identify constellations and predict their positions. That was crucial for navigation across the Sahara. Luna: So astronomy had practical applications beyond scholarship. Lucas: Absolutely. Caravans used the stars to navigate, and scholars like Ibn Ahmad provided the mathematical framework. They also used astronomy to determine prayer times and the direction of Mecca, which was essential for daily life. Lucas: But after the Moroccan invasion, this tradition went into decline. The scholars were scattered, the libraries looted, and the economy collapsed. It took centuries for Timbuktu to recover, and by then, the scientific tradition had largely been lost. Luna: It's tragic, but at least some of the manuscripts survived. And now they're being digitized and studied. Lucas: Yes, projects like the Timbuktu Manuscripts Project are working to preserve and digitize these texts. And as they're studied, we're learning more about figures like Ibn Ahmad. His work challenges the narrative that Africa was a passive recipient of knowledge from elsewhere. Lucas: So the next time someone says that pre-colonial Africa had no scientific tradition, you can point to Abou Bakr Ibn Ahmad al-Timbukti, who measured the Earth's circumference with astonishing accuracy, using instruments he likely made himself, in a city in the middle of the Sahara. Luna: That's a powerful counter-narrative. Thanks for sharing his story, Lucas. Lucas: My pleasure. And if you want to learn more, I'd recommend looking up the Mamma Haidara Library's online catalog. Some of Ibn Ahmad's manuscripts are available there, and you can see his diagrams and marginal notes for yourself. Luna: I might just do that. Until next time.