Cultural Confluences: Stories of a Thirteenth-Century Celestial Globe
When I first learned about astronomy, it seemed to start with the ancient Greeks and then jump to Copernicus. I hadn’t yet developed the spirit of inquiry to question the gap, let alone the end boundaries. As I got older and began to travel, I began to reflect on the smudged, smeared landscape of important ideas and how their pedigree of provenance seemed so artificial. Whereas clear crisp lines can help show division, life’s smudge marks can put things into a shared space and provide a form of unity. I think we need more of that today and it’s one of the reasons I wrote this piece. It also explains why I left smudges in the drawing more than chronological arrows leading from one theme to the next.
This piece has nothing to do with my work and comes from my own unrelated interest in art. I am not a trained art historian but find the stories of art and artefacts compelling nonetheless. I’m particularly interested in examples that show how ideas were formed at the confluence of different cultures. Whether those confluences were formed through trade, war or migration, they often leave behind a shared heritage of ideas that can tell future generations who they are.
One of my favourite artefacts is a beautiful brass celestial globe that bears the enigmatic inscription: “Made by the most humble in the supreme God, Muhammad ibn Hilal, the astronomer from Mosul, in the year 674” . Built in 1275 CE , the piece shows a continuity of ideas that spans over a thousand years and smudges cultural influences from Europe, the Middle East and Central Asia. It currently resides in the Islamic Gallery of the British Museum.
The globe features Greek constellations overlaid onto pre-Islamic Arabian star groupings that are oriented in left profile to show an Islamic view of the stars . The piece is the work of a Mosul-based astronomer who may have been displaced during the Mongol invasions that swept through Mesopotamia in the 13th-century . The Mongols destroyed the learning centres of the Abbasid Caliphate, only to commission new ones such as the Maragheh Observatory. The globe may have been used at the observatory, a place of learning that would spread new and refined ideas about the stars that would later nurture Renaissance Europe.
The Influence of Greek Astronomers on Arabic Astronomers
Islamic astronomers were heavily influenced by the Ancient Greeks, who in turn built on the work of even older cultures. The globe features 48 engraved constellations  which would have formed the classical Greek view of the stars. That view included the zodiac, which is a collection of shapes that evolved in Mesopotamia between 3200 and 500 BCE. The classical map also included Mediterranean-based constellations that date back to 2800 BCE. The origins of some constellations shown on the instrument are unknown [5, 6].
Some of the names inscribed on the globe acknowledge pre-Islamic star lore. For example, within the Ursa Major constellation, there are “the Gazelles”, “the Pond of the Gazelles”, “the Young of the Gazelles” and first, second and third “jumps” . These features are part of an Arabian story about a gazelle running away from a lion.
In the 8th and 9th centuries CE, Islamic astronomers tried to balance competing interests for using Greek and Arabic star lore in their work. Greek constellations were preferred for their more precise location of stars, but Arab constellations resonated more with the Arabic language that was at the core of Islam .
Classical Islamic star maps included both Bedouin star groupings and Ptolemaic constellations . Keeping with Islamic astronomical tradition, constellations were viewed as if looking into the Earth’s sky rather than viewed on Earth looking out. This is why the constellations on the globe appear in left profile .
Astronomy nurtured during the Islamic Golden Age
The scholarly spirit of drawing on multiple sources of ideas and blending them together was greatly supported in the Islamic Golden Age, an era that traditionally begins with the establishment of the Abbasid Caliphate in 750 CE  and ends with the Mongol sacking of Baghdad in 1258 CE .
The Abbasids created the House of Wisdom shortly after they founded Baghdad in 762 . Over five centuries, it would come to house the fruits of a bold knowledge acquisition effort. As Eamonn Gearon mentions in his course on this period , the goal of the early Abbasid caliphates was:
“…to translate every manuscript and book of any intellectual worth regardless of its geographical, cultural or religious provenance. Consequently the wisdom of the pagan Greeks was acquired just as greedily as that of Byzantine Christians, Persian Zoroastrians and Hindus from India.”
In this culture of scholarship, the Abbasid scholars made important advances. As Islamic scholars refined their methods for measuring the positions of celestial objects, they began to find that observations didn’t match earlier Greek models which were meant to explain the movement of stars and planets . Their findings were likely recorded and filed away in the House of Wisdom. But, one day in 1258 CE, librarians working in House of Wisdom would have heard commotion outside from a new invading force from the East. The storehouse of knowledge was about to be destroyed.
Mongol Invasions Displace then Collect Scientists and Artisans
Although the globe’s-maker Hilal was from Mosul, it may have been made and used in the Maragheh Observatory , whose ruins are located in Northern Iran and are now recognised in UNESCO’s Portal to the Heritage of Astronomy . How that observatory was created invites us to consider the Mongol invasion, a founding astronomer who advised for the Assassins, and the Mongol’s destruction of the House of Wisdom in Baghdad.
By the 1260s, Genghis Khan’s grandson Hulagu was leading Mongol armies across the Iranian plateau. In 1262, Genghis Khan’s Hulagu sacked Mosul after a year-long siege . The city was famed for its high quality metalworking craft, and some works of that school remain to attest to it [21, 22, 23]. We can only speculate whether Hilal, the maker of high quality instruments, had been displaced by the invasion or had managed to ply his craft in another city. But it would be another ten years before he would begin making the brass globe.
Hulagu’s main aim was to rule all Islamic lands as far as Egypt . Two major obstacles stood in his way: the Abbasid Caliphate based in Baghdad and the dreaded Assassins based in Alamut Castle  in what is now part of Northern Iran. In the land of the first he would encounter the home of the Globe Maker. In the land of the second he would encounter the future founder of a famous observatory the Khan would commission.
The Astronomer amongst Assassins
After conquering Mosul, Hulagu later turned to destroying a network of remote mountain castles maintained by the Assassins. They were part of the Nizari Ismailis, a breakaway group from the Ismailis branch of Shia Islam. The name may have been derived from hashish, which was apparently used by its followers. The first European report of them was probably written by Benjamin of Tudela in 1167 CE, who described them as a war-like sect who served a mysterious leader called the Old Man of the Mountain.
Headquartered at Alamut Castle, the Assassins ruled by fear through their use of espionage, guerrilla warfare, and targeted killings . They were feared by Crusaders and by the Abbasid Caliphate alike . But, in this story of the globe and one of its likely places of making, we are interested in one Assassin advisor holed up in a fortress under siege.
When Hulagu brought his troops to bear on the group’s mountain castles, the Ismailis were divided about how to they should respond: some wanted to surrender and some wanted to fight to the death. The leader of the sect, Rukn al-Din Khurshah, was apparently swayed by the opinion of his main astronomer Nasir al-Din Tusi, who felt surrender was the better option because the stars were inauspicious.
Nasir al-Din Tusi was sent to Hulagu to negotiate a surrender with the besieging Mongol army. Khurshah believed that when he surrendered his castle fortresses, he would serve the Khan. But after surrendering Alamut castle and helping to dismantle other Ishmaili fortifications, Hulagu had him murdered .
By the time Khurshah had been killed in 1256 CE, the Assassins had been neutralised as a major threat to the Mongols. But Nasir al-Din Tusi eagerly accepted a new position as one of Hulagu’s scientific advisors , and he would go on to become the most famous 13th-century Islamic scholar. It is unclear whether Tusi later witnessed the Sack of Baghdad, but apparently his interests included combating Mongol savagery and saving the lives of scholars .
A Knowledge Centre Destroyed, a Knowledge Centre Created
After Hulagu destroyed the Assassin strongholds, he attacked Baghdad in 1258 CE. The Mongols slaughtered much of the city’s population and destroyed the House of Wisdom . It is a point of glaring contradiction that the same leader who destroyed the House of Wisdom would eventually commission new centres for knowledge such as the Maragheh Observatory.
Like many Mongol rulers, Hulagu was interested in astronomy, especially for its use in making predictions that might influence judgements about strategic military operations. Not only had Tusi convinced Hulagu to spare his life at Alamut, but he also persuaded him to build a new observatory at Maragheh in 1259 CE .
It cannot be proven that the brass globe was definitely made at the Maragheh Observatory. However, Hilal’s home city of Mosul was probably still recovering from the invasion of 1262 CE, and it may not have been a centre that would support a skilled astronomer. Mongol leaders were known to relocate skilled citizens from conquered lands , and a similar globe built in 1279 CE was known to come from there . The Mongols may have sent Hilal to the Observatory, which was in the process of becoming a prestigious scientific research institute.
It was here that facilities were built to provide highly accurate measurements of planetary movements. The Observatory became a great hub for scientific collaboration , and it contained a library that was thought to contain 400,000 volumes of work . The findings of the scholars at Maragheh would have an impact that reached far beyond the steppe lands in Europe.
Influence of Islamic Astronomers on Medieval European Astronomers.
Although Islamic scholars had initially based much of their astronomical theory on the writings of Ptolemy, it was becoming increasingly difficult for them to fit their calculations to the earth-centric model he proposed. The scholars at Maragheh did not have telescopes, yet they developed sophisticated mathematical techniques that would influence astronomy for centuries afterwards .
The planetary models developed at Maragheh Observatory, and later at the Samarqand Observatory, would be communicated to Europe, and provide mathematical tools that would let Copernicus create a heliocentric model of the universe .
Returning to my initial impression of the history of astronomy, the time frame between Ptolemy and Copernicus has now become more smudged across different cultures — and is far more interesting.
Stories of the Celestial Globe
When I look at this beautiful scientific instrument in the British Museum, my imagination conjures a loosely connected collection of mental images.
In some pockets I see foundational knowledge being developed. I imagine mud brick Sumerian buildings where people are trying to graft zodiac shapes into the night sky. In Roman-occupied Egypt, Ptolemy is carefully working on more calculations and filing them away in whatever part of the Library of Alexandria may have remained. Meanwhile, Bedouin caravans pause and people look up at the night sky as if they are glancing at a road map. I see Hindu numbers drifting through the Middle East before transforming into Arabic numbers being used in celestial calculations (and as I read more there are more pockets coming from India).
In other pockets I imagine the House of Wisdom and think of shelves of scrolls archiving ideas drawn from all over the Ancient World. As the hoof steps get louder the House crumbles and I imagine displaced astronomers being collected in a high flat area with an observatory being built. As the Mongols solidify trading corridors in their expanding empire, ideas pulse overland on dusty roads and over water to the shores of medieval Europe.
When I first tried to map all the pockets into a drawing, I was inclined to put all sorts of chronological arrows leading from one source to another. But I largely gave up and became more content leaving smudged patches of graphite and charcoal to highlight the messy transmission of ideas that may better reflect a shared heritage of accumulated knowledge.
However knowledge was gathered or created in the Golden Age of Islam, the legacy of Arabic contributions to astronomy remains immense. Two thirds of named stars have Arabic origins, and I labelled a few examples in the constellation of Orion. Or is it al-Jawza? Or is it just a group of stars that have twinkled our curiosity to name and draw from our own cultures.
 Brass celestial globe, made by Muhammad ibn Hilal, Google Arts and Culture, https://artsandculture.google.com/asset/brass-celestial-globe-made-by-muhammad-ibn-hilal/KAHRR2UTPHZu0A?hl=en, Accessed 15 February 2021
 Celestial Globe, British Museum, https://www.britishmuseum.org/collection/object/W_1871-0301-1-a-b,Accessed 15 February 2021
 13th century celestial globe. British Museum, Youtube. URL: https://www.youtube.com/watch?v=gYa1Jg-7Elc&vl=en-GB, Accessed 15 February 2021
 Akbarnia, Ladan. The Islamic World: A History in Objects. Thames and Hudson, 2018, p 49.
 The Origin of the Zodiac. Ancient Wisdom, http://www.ancient-wisdom.com/zodiac.htm, Accessed 15 February 2021
 Lebling, Robert. 12 Things Twitter Won’t Tell You About Zodiacs. AramcoWorld. November 2017.
 Our Arabic Heritage in the Celestial Vault. Muslim Heritage, May 2008, https://muslimheritage.com/our-arabic-heritage-in-the-celestial-vault/
 Saliba, G. Astronomy: Reaching for the Stars. World Digital Library. . URL: https://www.wdl.org/en/themes/islamic-science/astronomy/, Accessed 15 February 2021.
 Book of Fixed Stars. Wikipedia, https://en.wikipedia.org/wiki/Book_of_Fixed_Stars, Accessed 15 February 2021.
 carlesdorce.The Mathematical Tourist. 09/08/2013. Web Site. URL: https://themathematicaltourist.wordpress.com/2013/08/09/the-british-museum/, Accessed 15 February 2021
 Britannica, The Editors of Encyclopaedia. “ʿAbbasid caliphate”. Encyclopedia Britannica, 5 Mar. 2020, https://www.britannica.com/topic/Abbasid-caliphate. Accessed 15 February 2021.
 Gearon, Eamonn. The Mongol Sack of Baghdad in 1258, The Great Courses Daily, February 9, 2017, https://www.thegreatcoursesdaily.com/the-mongol-sack-of-baghdad-in-1258/
 Bahry, Louay and Marr, Phebe A.. “Baghdad”. Encyclopedia Britannica, 10 Jan. 2020, https://www.britannica.com/place/Baghdad. Accessed 15 February, 2021.
 Gearon, Eamonn, The History and Achievements of the Islamic Golden Age, Lecture 1, The Great Courses, https://www.thegreatcourses.com/courses/the-history-and-achievements-of-the-islamic-golden-age, Accessed 15 February, 2021.
 Britannica, The Editors of Encyclopaedia. “Almagest”. Encyclopedia Britannica, 21 Jun. 2002, https://www.britannica.com/topic/Almagest. Accessed 15 February 2021.
 Maragheh Observatory, Maidan Project, https://madainproject.com/maragheh_observatory, Accessed 15 February 2021.
 Category of Astronomical Heritage: tangible immovable
Maragheh observatory, Iran, Portal to the Heritage of Astronomy, UNESCO, https://www3.astronomicalheritage.net/index.php/show-entity?identity=29&idsubentity=1, Accessed 15 February 2021
 Lewis, Bernard. The assassins. Basic Books, 2008.
 Hulagu Khan. Wikipedia. Web site. URL: https://en.wikipedia.org/wiki/Hulagu_Khan, Accessed 15 February 2021
 Mosul: Iraq’s beleaguered city, BBC, 18 October 2006, https://www.bbc.co.uk/news/world-middle-east-37676731, Accessed 15 February 2021
 Candlestick with Enthronement Scene, second quarter of 13th century, https://www.metmuseum.org/art/collection/search/444563, Accessed 15 February 2021
 ewer, British Museum, Accessed 14 February 2021, https://www.britishmuseum.org/collection/object/W_1866-1229-61, Accessed 15 February 2021
 Metalwork bag. Courtauld Gallery. Web Site. URL: http://www.courtauldprints.com/image/1132602/mosul-northern-iraq-metalworker-metalwork-bag, Accessed 15 February 2021
 Tesch, N. Who were the Assassins? Encyclopaedia Britannica. 09/02/2016. Web Site. URL: https://www.britannica.com/demystified/who-were-the-assassins
 Britannica, The Editors of Encyclopaedia. “Naṣīr al-Dīn al-Ṭūsī”. Encyclopedia Britannica, 22 Jun. 2020, https://www.britannica.com/biography/Nasir-al-Din-al-Tusi. Accessed 15 February 2021
 Nasir al-Din Tusi (1201–1274). Internet Encyclopedia of Philosophy: A Peer-Reviewed Academic Resource. Web Site. URL: http://www.iep.utm.edu/tusi/, Accessed 15 February 2021
 House of Wisdom. Wikipedia. URL: https://en.wikipedia.org/wiki/House_of_Wisdom, Accessed 15 February 2021
 Science in the Golden Age — Astronomy: The Science of the Stars. Al Jezeera, Youtube, https://www.youtube.com/watch?v=3cVfyurIFvM, Accessed 15 February 2021
 Maragheh observatory, Wikipedia, https://en.wikipedia.org/wiki/Maragheh_observatory, Accessed 15 February 2021
 Case Study 10.1: The Maragheh Observatory, Iran, Portal to the Heritage of Astronomy, UNESCO, https://www3.astronomicalheritage.net/images/astronomicalheritage.net/media/ahp_entities/entity000029/ch10cs1.pdf, Accessed 15 February 2021