The Islamic world: from Mecca to Baghdad and Córdoba

The English words algebra and algorithm both come from one 9th-century scholar in Baghdad: from the title of his book and from his name, al-Khwarizmi.

A new faith in Arabia

According to Muslim tradition, around 610 Muhammad, a merchant of Mecca in western Arabia, began to receive revelations that were later gathered as the Quran. His preaching of one God met hostility in Mecca, and in 622 he and his followers moved north to the town of Yathrib, afterwards called Medina, the city of the Prophet. This move, the hijra, marks year 1 of the Islamic calendar. By the time Muhammad died in 632, much of Arabia had accepted Islam and his leadership. His successors, the caliphs (from khalifa, successor), led Arab armies out of Arabia with great speed. Within about twenty years they had taken Syria, Egypt and Iraq from the Byzantine and Persian empires, and the Sasanian Persian empire collapsed altogether.

Umayyads and Abbasids

In 661 the Umayyad family made Damascus the capital of a caliphate that, within a century, stretched from Spain to Central Asia. The Umayyad caliph Abd al-Malik built the Dome of the Rock in Jerusalem, completed in 691 or 692, and introduced coins with only Arabic writing on them. Arab and Berber armies crossed into Spain in 711, and their advance into Gaul was turned back between Poitiers and Tours in 732 (unit 1). In 750 a new dynasty, the Abbasids, overthrew the Umayyads. One Umayyad prince, Abd al-Rahman, escaped to Spain and made himself ruler at Córdoba in 756; his family ruled there until 1031, and its Great Mosque was begun in 785. The Abbasid caliph al-Mansur founded a new capital, Baghdad, on the Tigris in 762. It was laid out as a round city with the palace and the main mosque at its centre.

Paper and the House of Wisdom

Paper, a Chinese invention, spread into the Islamic world in the 8th century, and by the end of that century it was being made in Baghdad. Paper was much cheaper than parchment or papyrus, and books multiplied. Abbasid caliphs and wealthy families paid translators to put Greek works of medicine, astronomy, mathematics and philosophy into Arabic, often by way of Syriac. A library and translation centre in Baghdad known as the House of Wisdom, Bayt al-Hikma, is linked with this movement, although historians now think the translating went on in many households and cities rather than in one building. Euclid, Ptolemy, Galen and Aristotle were all read in Arabic long before most of their works were available in Latin, and Arabic scholars added commentaries, corrections and new results of their own.

Scholars whose names stayed

Al-Khwarizmi, who worked in Baghdad in the early 9th century, wrote a book on solving equations whose title included the word al-jabr, “restoring”, the source of algebra. A Latin version of his book on Indian numerals began with the words “Dixit Algorizmi”, al-Khwarizmi said; it helped spread the digits 0 to 9 in Europe and gave us the word algorithm. Ibn al-Haytham, working in Cairo in the early 11th century, argued in his Book of Optics that we see because light enters the eye, and he tested his ideas with experiments. Ibn Sina (980 to 1037), known in Latin as Avicenna, wrote the Canon of Medicine. Gerard of Cremona translated it into Latin in 12th-century Toledo, and according to the Library of Congress it stayed in the curriculum of European medical students until the late 17th century.