In February 1258 a Mongol army under Hulagu, a grandson of Genghis Khan, broke into Baghdad after a short siege. The city was sacked for days, and al-Musta'sim, the last Abbasid caliph to rule from Baghdad, was put to death. Later chroniclers wrote that the Tigris ran black with the ink of books thrown into it. Such images may be exaggerated, and estimates of the dead range from tens of thousands to figures in the hundreds of thousands that are probably far too high, but the destruction was real, and the end of the caliphate in Baghdad was a profound shock.

A long fragmentation

The caliphate Hulagu destroyed was already a shadow. From the ninth century, provinces slipped away under local dynasties; in 945 the Buyids, a Persian Shia family, took control of Baghdad and left the caliph as a figurehead, and in 1055 the Seljuk Turks replaced them. Rival caliphates arose: the Fatimids, an Ismaili Shia dynasty, founded Cairo in 969 and made it a center of learning, and the Umayyads of Cordoba claimed the title too. Crusaders took Jerusalem in 1099. The Golden Age was never the work of one unified state; much of its best work came after political unity had broken down, in rival courts competing for scholars.

Nor did the Mongols end everything. In 1260 the Mamluks of Egypt defeated a Mongol army at Ain Jalut, halting the Mongol advance, and Cairo and Damascus flourished. Hulagu himself funded the Maragha observatory under al-Tusi, who had entered his service, and within a few decades the Mongol rulers of Iran converted to Islam.

The decline debate

Many older Western histories described an Islamic civilization that blazed brightly and then stagnated, blaming 1258, religious conservatism after al-Ghazali, or a supposed hostility of Islam to reason. Many historians now call this the "decline thesis" and criticize it for ignoring later achievements. The Ottoman, Safavid and Mughal empires built great states, cities and monuments between the fifteenth and eighteenth centuries. Ulugh Beg built a major observatory at Samarkand in the 1420s. In 1377 the North African scholar Ibn Khaldun completed the Muqaddimah, which explained the rise and fall of dynasties through asabiyya, or group solidarity, a work often seen as an early form of sociology.

Yet a real question remains. By around 1700, Western Europe had pulled ahead in science, technology and wealth. Explanations differ. Some economists point to law: Timur Kuran argues that Islamic partnership and inheritance rules kept firms small and short-lived, while waqf endowments locked capital into fixed uses. The political scientist Ahmet Kuru stresses an alliance between religious scholars and military states that sidelined merchants and independent thinkers. Others emphasize trade shifting to the Atlantic, or warn against judging a civilization only by the yardstick of European science. Historians are still arguing, and single-cause stories deserve suspicion.

The road to Europe

Arabic learning entered Latin Europe by several roads. Toledo was one. In Norman Sicily, Arabic, Greek and Latin cultures met at the court of Roger II, for whom the geographer al-Idrisi made a celebrated world map in 1154. Constantine the African, a monk at Monte Cassino in the late eleventh century, translated Arabic medical works into Latin. The Englishman Adelard of Bath translated al-Khwarizmi's astronomical tables. Leonardo of Pisa, called Fibonacci, learned Indian numerals as a boy in North Africa and promoted them in his Book of Calculation of 1202.

Ibn Rushd's commentaries made him so central to the study of Aristotle in the universities that Latin writers called him simply "the Commentator". Dante placed him among the virtuous non-Christians in Limbo, and in Longfellow's 1867 translation of the Inferno the line reads: "Averroes, who the great Comment made." Some Paris teachers who followed his readings on points such as the eternity of the world were condemned by the bishop of Paris in 1270 and 1277, and Thomas Aquinas both relied on Ibn Rushd and argued against him.

Two cautions apply. First, the word "transmission" can make Arabic scholars sound like a delivery service carrying Greek parcels to Europe. In fact they changed what they carried: Europeans received algebra, Ibn Sina's medicine and Ibn Rushd's Aristotle, not just older Greek texts. Second, the European Renaissance drew on many sources, including Byzantine scholars and Greek manuscripts.

Worked example: testing two slogans

You see two slogans online. One says, "Without the Islamic Golden Age there would be no modern science." The other says, "Islamic civilization only copied the Greeks." Test each against the evidence. Against the second: algebra as a systematic subject, al-Razi's clinical observations, Ibn al-Nafis's account of the lungs and the Maragha models were original. Against the first: modern science also drew on Greek, Indian, Chinese and later European work, and claims about what would never have happened cannot be proven. A fair statement might be: "Scholars of the Islamic world made major original contributions and passed on a body of learning that Latin Europe used heavily." It is less exciting than either slogan, and much closer to the truth.