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Power And Curiosity: How The Abbasid Caliph Al-Mamun Pushed The Boundaries Of Scientific Knowledge 

Born in 786, al-Mamun was the son of the legendary Caliph Harun al-Rashid, whose adventures feature in lurid detail in One Thousand and One Nights. Harun appointed Jafar, a member of the cultured Persian Barmakid family, as Mamun’s tutor, who instilled a profound love of learning in his young pupil that continued throughout his life.

Well versed in all aspects of Greek philosophy and learning, Mamun even claimed that Aristotle had visited him in a dream, and he certainly adopted the great philosopher’s fascination with the natural world and how it works.

A gold Abbasid dinar, struck during the reign of al-Mamun

When Mamun became Caliph (after a bloody civil war with his brother al-Amin, Harun’s chosen heir) he put his enormous power and wealth in the service of scientific discovery. His personal interest and curiosity lay at the heart of this endeavour. When on campaign in Egypt he commissioned scholars to try to decipher hieroglyphs (something that was not finally achieved until after the discovery of the Rosetta Stone in 1799), he forced entry into the Great Pyramid of Khufu and was disappointed to discover that it had already been plundered – apparently all that was left was a sarcophagus of bones and a jar of gold.

Back in his capital city Baghdad, he and erudite members of the elite paid translators in bags of silver to carry out vital work transmitting ideas from ancient Greece, India, Persia and Syria into the Arabic tradition. Obtaining copies of these books was a vital component of the huge flowering of learning in Baghdad during this period, Mamun himself wrote to the Emperor in Constantinople asking him to send ancient texts so he could have them translated into Arabic.

A 16th century image of astronomers using a wide array of instruments in an observatory.

He also paid for original scientific research, setting up the first observatory in the Islamic world so that his astronomers could record accurate observations of the celestial bodies, later building another one in Damascus so that data from the two could be compared. Mamun’s palaces thronged with scholars engaged in lively debates, he encouraged them to challenge one another and the ancient texts they studied. He was demanding and arrogant – no question was too big or too difficult, he wanted to know everything, a desire that culminated in a project to measure the circumference of the globe. Ancient astronomers had already made these calculations, using the stars to work out how much one degree of the circumference measured and then multiplying it by 360, the problem was that there was no record of the size of their units of measurement. Mamun’s astronomers set off in the middle of the night across the flat plain of Sinjar, one group walking due north, the other due south, until they had measured one degree of the earth, before walking back towards one another carefully counting the distance. The resulting average, when multiplied by 360, gave them a total of 24,500 miles – a mere 400 miles off the accepted distance measured by modern science. This was an exceptional feat of scientific brilliance, but, typically, Mamun was not satisfied – he sent them all off to the Syrian desert so that they could repeat the experiment and check their answer. Under Mamun’s influence, scientific discovery blossomed in the Islamic Empire; his vision, curiosity and charisma helped fuel one of the greatest intellectual epochs of all time. 

In The Map of Knowledge, I follow the books translated and written in Mamun’s Baghdad as they travel across the Mediterranean and later pass into Latin Europe, where, in fifteenth century Venice, they are printed for the first time and their legacy is assured. 


Violet Moller is a historian and writer who lives in Oxford. The Map of Knowledge received a prestigious RSL Jerwood Award in 2016.

She will be speaking at Chalke Valley History Festival on Thursday 27th June 2019 about The Map Of Knowledge: How Classical Ideas Were Lost And Found. Tickets are available here.