Write down the year. Nine hundred and ninety nine, say, and then add one.
You have just done something no Roman could do easily and no Greek mathematician did at all. You used a place value system in which the position of a digit carries its magnitude, and a symbol for nothing, so that carrying happens automatically and the whole operation takes a second. Try the same sum in Roman numerals and you will see why ancient arithmetic was done on a counting board by specialists.
The system was developed in India. It reached the Latin west through Arabic, in books written by scholars working in Baghdad, Cairo and Córdoba, and it took European merchants about three centuries to adopt it fully because the older method had an entrenched guild behind it and because a symbol that could be altered with a stroke of the pen worried bankers.
That is the shape of this chapter in miniature. Something is invented in one place, refined in a second, transmitted through a third, and arrives in Europe as though it had always been there.
Islam began in western Arabia in the early seventh century. Within a hundred years of the Prophet’s death in 632, states professing it governed from the Atlantic to Central Asia, which is one of the fastest political expansions on record.
The previous chapter gave part of the reason: the two empires in the way had just fought each other to exhaustion, and the populations of Syria and Egypt had been alienated from Constantinople by two centuries of theological quarrels. Conquest was often a matter of terms negotiated with a city rather than a massacre.
In 711 an army crossed from North Africa into Spain and destroyed the Visigothic kingdom in a single campaign. Within a few years Muslim rule extended over most of the peninsula. Raiding parties crossed the Pyrenees and were checked in central France in 732 by a Frankish army, a battle later treated as the salvation of Europe and now generally regarded as a raid turned back rather than an invasion stopped.
What settled in Spain was a state, not a garrison. When the ruling dynasty in the east was overthrown, a surviving prince fled to Spain and founded an independent emirate at Córdoba, which in the tenth century declared itself a caliphate. At its height Córdoba was among the largest cities in the world, with paved and lit streets, running water, hundreds of public baths, and a library whose catalogue alone is said to have run to many volumes.
Sicily was taken over the ninth century and held for about two hundred years, and it matters for the same reason Spain does: it became a place where Arabic, Greek and Latin were all in use at once.
The legal position of Christians and Jews under Muslim rule was defined and it was not equality.
They were protected communities. They could practise their religion, run their own courts for their own affairs, and were not to be forcibly converted. In exchange they paid a tax that Muslims did not pay, were barred from certain offices, could not build new places of worship without permission, and were subject to restrictions on dress, on riding, and on the height of buildings that varied enormously by time and ruler.
In practice this ranged from comfortable to lethal. There were long periods when Jewish and Christian officials served at the highest levels of Muslim courts in Spain, when Hebrew poetry flourished as it had not for centuries, and when Arabic was the shared literary language of all three communities. There were also pogroms, including one in Granada in 1066 in which a large part of the Jewish population was killed, and there were periods under stricter North African dynasties in the twelfth century when Jews and Christians were given the choice of conversion, exile or death.
The Spanish word for the coexistence, convivencia, has become a battleground. One tradition presents al-Andalus as a tolerant multicultural paradise, and it tends to quote the good centuries and skip the rest. Another insists the whole idea is a myth and that subordination is subordination, and it tends to do the reverse.
The defensible position is duller than either. A legally subordinate but protected status is a real and important thing, better than the alternatives available in most of Christian Europe at the same date, where Jews had no such standing at all and were expelled from England in 1290, from France repeatedly, and from Spain itself in 1492. And it was still subordination, and it broke down into violence more than once.
The intellectual story has two stages, and confusing them is the commonest error.
The first stage happened in the east. From the late eighth century, under state patronage in Baghdad, Greek scientific and philosophical works were systematically translated into Arabic, often via Syriac. This was not antiquarianism. Rulers wanted medicine, astronomy for the calendar and for prayer times, mathematics for surveying and inheritance law, and logic for argument. Aristotle, Euclid, Ptolemy, Galen, Hippocrates and Archimedes were rendered into Arabic by paid professionals with access to manuscripts.
Then came original work, and it is not a footnote. A ninth century scholar in Baghdad wrote a systematic treatise on solving equations whose title gives us the word algebra, and whose own name, latinised, gives us the word algorithm. An eleventh century scholar in Cairo wrote a book on optics that got vision fundamentally right, argued from controlled experiments, and was the standard European authority for six hundred years. A Persian physician compiled a medical encyclopaedia that was a set text in European universities into the seventeenth century. A twelfth century judge in Córdoba wrote commentaries on Aristotle so thorough that Latin scholastics referred to him simply as the Commentator.
The second stage is the one that concerns Europe directly. In 1085 the Christian kingdom of Castile took Toledo, a city full of Arabic manuscripts and of people who could read both Arabic and Romance. Over the following century Toledo, and Sicily under its Norman kings, became translation centres where teams rendered Arabic works into Latin.
The scale was large. One translator working at Toledo is credited with something like seventy titles. What crossed included Aristotle’s scientific works, which the Latin west had largely not had, Euclid, Ptolemy’s astronomy under its Arabic derived title, the medical corpus, and the mathematics. The universities described in a later chapter were founded just as this material arrived, and much of what they argued about for the next two centuries was how to reconcile it with Christian doctrine.
Alongside the philosophy, a set of ordinary things that changed daily life more.
Paper. Made in China, learned by Muslim craftsmen in Central Asia in the eighth century, manufactured across the Islamic world, and made in Europe first in Muslim Spain. It is perhaps a fiftieth the cost of parchment and it does not require killing anything. Everything in the later chapters about printing, bureaucracy and literacy depends on paper being available first.
Irrigation and crops. Techniques for lifting and distributing water, and with them sugar cane, rice, cotton, citrus, aubergines, spinach and hard wheat, spread west along the Mediterranean. A significant slice of what people now think of as traditional Spanish and Italian agriculture arrived this way.
Navigation and instruments. The astrolabe reached Europe through Spain, along with tables of astronomical data, improved trigonometry and the compass rose.
Music and the crafts. The lute takes its name and its shape from an Arabic instrument, and so does the guitar at one remove. Techniques in glass, ceramics, inlaid metalwork, silk weaving and leather moved north with the objects themselves, and the names of several European textiles are the names of the cities that first made them.
And the vocabulary, which is the fossil record of the transfer. Algebra, algorithm, alcohol, alkali, alchemy, cipher, zero, admiral, arsenal, tariff, magazine, sugar, syrup, cotton, orange, lemon, apricot, artichoke, saffron, mattress, sofa, guitar. When a language borrows the word with the thing, it is telling you where the thing came from.
Christian kingdoms in the north pushed south over four centuries, in a process that later writers packaged as a single religious reconquest and which was, for most of its length, ordinary medieval warfare with shifting alliances that regularly crossed the religious line.
Christian rulers hired Muslim troops and Muslim rulers hired Christian ones. The mercenary whose legend became Spain’s national epic spent part of his career in the service of a Muslim king. Frontier lords made treaties, took tribute from the other side, and fought coreligionists as readily as anyone else.
It hardened over time, partly under the pressure of stricter North African dynasties arriving to reinforce the Muslim side and of crusading ideology arriving to reinforce the Christian one. By the thirteenth century most of the peninsula was in Christian hands, leaving one kingdom in the south, which survived as a tributary for another two hundred and fifty years.
Granada fell in January 1492. In March of the same year the Spanish crowns ordered the expulsion of Jews who would not convert. Within a decade the same choice was imposed on Muslims, and a century later the descendants of those converts were expelled as well, on the grounds that their conversion had not been sincere.
It is worth pausing on what was lost administratively, because it is the kind of damage that does not photograph. Granada and Valencia had irrigation systems built and maintained over centuries by communities that were now removed. Some of the works were kept up by the newcomers and some silted and failed, and parts of southern Spain took a very long time to recover the agricultural output they had had under the previous management.
In October of 1492 an expedition funded by the same monarchs, in part with the proceeds of the conquest, made a landfall in the Caribbean. The two events are usually told as separate stories. They were the same year, the same court, and to a considerable extent the same budget.
Firm: the transmission. We have the Arabic texts, the Latin translations, the names of translators, and in many cases manuscripts showing the intermediate stages. The vocabulary is independent physical evidence in the language itself.
Firm: the legal framework of protected status, which is documented in law and in surviving contracts, tax records and court cases.
Soft: Córdoba’s size and its library. The famous figures come from later Arabic writers who had reasons to make it magnificent, and the four hundred thousand volume library is a number that should be treated as a boast rather than a catalogue.
Contested: the character of coexistence, as discussed above. Be suspicious of any account of al-Andalus, in either direction, that never mentions the evidence inconvenient to it.
Contested: how much difference the transmission made. A strong version says medieval European science was essentially an Arabic inheritance. A weaker version notes that the Latin west also had its own developing traditions and that what it did with the material was its own. The honest summary is that the west received an enormous body of work it had lost or never had, at exactly the moment it had built institutions capable of arguing about it, and that both halves of that sentence matter.