Al-Idrisi completes the ‘Book of Roger’

Al-Idrisi was born in Ceuta in 1100 into a branch of the house of the Idrisids, studied in Córdoba and travelled widely — to Asia Minor at sixteen, along the southern coast of France, to England, across Spain and Morocco. Around 1138 — no primary source gives the year — Roger II invited him to Palermo; the historian Tadeusz Lewicki suggested that the king valued him less as a geographer than as a nobly born pretender who might serve his Mediterranean ambitions. Roger, whose skill in mathematics al-Idrisi praised, set him to produce an up-to-date description and map of the world.

According to al-Idrisi's preface, the work went on for about fifteen years. Finding the books of earlier geographers contradictory, the king had well-travelled informants questioned singly and together and kept only what they agreed on; their data were plotted on a drawing board with iron instruments, and the resulting map was engraved on a disc of pure silver weighing 400 Roman pounds — some 134 kg. The book that explains it, completed in the first ten days of January 1154 (Shawwal 548), divides the inhabited world from the equator to the north into Ptolemy's seven climes, and each clime into ten sections from west to east; each section has its map — seventy in all, with south at the top — and a description of its towns, roads and distances, peoples, products and trade. Besides Ptolemy and Orosius, al-Idrisi drew on Arabic geographers such as Ibn Khurradadhbih, al-Mas'udi and Ibn Hawqal.

The silver map is lost — it is said to have perished in the uprising against Roger's son in 1160–1161, though there is no firm evidence — but the book survives in some ten manuscripts, the oldest from about 1300. It is richest for the Mediterranean, Europe and North Africa, yet it also describes Ghana as a powerful Muslim kingdom on the 'Nile of the Blacks', Rus' with more than twenty towns and the junks trading from Chinese ports. Extracts of the Arabic text were printed in Rome in 1592 and a Latin abridgement in Paris in 1619; later geographers and historians of the Islamic world, Ibn Khaldun among them, used it, while the orientalist Ignaty Krachkovsky judged its maps a step back from the earlier Arabic attention to latitude and longitude. After Roger's death al-Idrisi served his son William I and seems finally to have returned to North Africa, where he died in 1165 or 1166, probably in Ceuta.