Mathematical Geography and Cartography in Islam and their Continuation in the Occident, Vol. I. Historical Presentation
- Fuat Sezgin,
- translated by Guy Moore &
- Geoff Sammon
Few books in the historiography of science have single-handedly created a revolution in their subject, but this one just might. It is the result of a 15-year effort by the renowned Arabist and science historian Fuat Sezgin. Originally, the book was to be just another volume in the author's History of Arabic Literature series, begun in 1967, in which a scholarly historical introduction is followed by a list of authors and critical assessments of their works. Mathematical Geography and Cartography in Islam and their Continuation in the Occident retains this format, but the usual introduction is expanded into two massive volumes of ‘historical presentation’, plus a lavishly illustrated atlas with 209 maps (many in colour). It was originally published in German in 2000, but an English translation of Volume 1 is now available and Volume 2 will follow shortly, along with the final ‘authors’ section of the German original.
While working on the book, Sezgin found that conventional treatments of the history of mathematical geography and cartography had failed to take into account nearly half of the available material, and it is the narration and analysis of this that fills the bulk of these volumes. He first became aware that something was seriously amiss when he heard about the sudden appearance of some portolan maps, or navigational sea charts, from around 1300, and some remarkably accurate longitude and latitude data in European maps of parts of Asia, dating from times when no European had been there to take any measurements.
A clue to the puzzle lay in the discovery of an annotated version of Masalik al-abşar fi mamalik al-amşar by Ibn Fadlallah al-Umari, a representation from 1340 of a lost map of the world prepared by the geographers of the Abbasid caliph al-Ma'mun in the eighth century. The version by al-Umari was drawn on a pre-existing graticule with a globular projection, and not vice versa as had previously been assumed — I can vouch for this, having checked the original myself. This helped Sezgin interpret the data on geographical coordinates that originally accompanied the Ma'munic map. Sezgin found the data preserved in the book Sûrat al-ard from the early ninth century, which has commonly, but mistakenly, been considered to be an original work of Abu Ja'far al-Khwârizmî. It is now thought to be a simple register of Ma'munic location data.
Sezgin argues that the collection of all these data necessitated new fieldwork and must have required a large group of observers, rather than being revisions by one hypothetical Syriac author of a Ptolemy translation, as Hans von Mzik had proposed. Sezgin's reconstruction of the Ma'munic map, put together using the only two preserved versions of its coordinate data, shows that the Ma'munic geographers had reverted to the earlier idea, proposed by the Greek scholar Eratosthenes, that the world consisted of inhabited land surrounded by the ocean, as opposed to Ptolemy's view in which oceans appeared as giant lakes. For example, the map shows the Arabic error of considering the Malaysian peninsula to be a vast elongation of southern China, but separated from Africa, as seen in al-Umari's map. An even older version of the map discovered by Joseph Needham corroborates Sezgin's reconstruction.
Once the Ma'munic improvement on Ptolemy was correctly reconstructed, it led to a search for other geodetic improvements, both in methods and in results, by Islamic mathematical geographers and cartographers. Sezgin documents in great detail how the Ptolemaic ‘long Mediterranean’ was shortened almost to its length today by fixing the positions of Baghdad and Toledo; how the Caspian Sea gradually acquired its correct outlines; how, by a combination of dead reckoning and trigonometry, the Arabs managed to get to grips with longitude at sea; and finally, how the distance between Ghazna and Baghdad was measured with astonishing precision in the eleventh century using astronomical observations and spherical trigonometry.
Sezgin then documents the influence of these achievements in Europe. A number of Western authors, including Marco Polo, Dante, the astronomer Johannes Kepler and the cartographer Nicolas Sanson, seem to have been informed by Arabic–Islamic geography. Sezgin shows how the Muslim maps led to the portolans, as they had to Portuguese maps of the Indian Ocean. He documents and discusses in great detail the information that Muslim geographers gathered on Asia, the Indian Ocean, the Malay Archipelago, the Mediterranean and Africa. He also details the new geodetic methods they discovered and the numerous coordinate tables they generated, which influenced European maps well into the eighteenth century.
The abundance of material brought together in this book is truly awesome. The three handsomely produced volumes are thoroughly indexed. With so many novelties, Sezgin's book will no doubt be controversial. But therein lies an added value: it will provoke an even more thorough search for additional data on the history of a subject that had long stagnated.