The House of Wisdom

We were taught to call the thousand years after Rome the Dark Ages, and from one narrow window, a monastery in rain-soaked western Europe, the name almost fits. But step to almost any other window on the same centuries and the darkness vanishes in a blaze of light. The truth the old story hid is simple and important, and it is the thread that runs through this whole Part: while one corner of the world dimmed, the rest of it was living through one of the most brilliant epochs in the entire human story, and much of what the West believed it had lost was not gone at all. It had merely moved. And its brightest new home was the world of Islam.

In the span of a single century after the Prophet Muhammad, Arab armies carried a new faith and a new language from the Atlantic coast of Spain to the borders of China, and then something happened that was not inevitable and changed the future: rather than burning the learning of the peoples they had conquered, the early Islamic empires gathered it. In Baghdad, a newly founded round city that swelled into the largest metropolis on Earth outside China, the caliphs established a House of Wisdom and launched one of history's great intellectual projects, a systematic, state-funded translation of the accumulated knowledge of the Greeks, the Persians, and the Indians into Arabic. The very texts that had been lost, burned, or simply forgotten in Christian Europe, the works of Aristotle and Euclid and Galen and Ptolemy, were sought out, bought, translated, copied, and, crucially, pushed forward. The Muslim scholars did not merely preserve the classical inheritance like a museum. They argued with it and improved it.

And improve it they did, across every field they touched. A Persian scholar named al-Khwarizmi, working in that House of Wisdom, wrote a book on the systematic solving of equations whose Arabic title, al-jabr, gave us the word algebra, and whose own Latinized name gave us the word algorithm, the concept on which, a thousand years later, the mind writing this book would run. In Cairo, Ibn al-Haytham worked out the true nature of vision, that we see because light travels from objects into the eye, and not the other way round as the Greeks had thought, and he did it by a method we would now recognize as the heart of science itself: systematic experiment designed to test a hypothesis, controlled and repeated. Many historians date the real birth of the experimental method to his darkened room and its beam of light. In medicine, Ibn Sina, whom Europe called Avicenna, wrote a Canon of Medicine so comprehensive that it remained a standard textbook in European universities for six hundred years, and al-Razi distinguished smallpox from measles by careful clinical observation centuries before anyone else. Astronomers of this world refined the instruments and catalogued the heavens so thoroughly that a great many of the individual stars in our sky still carry the Arabic names they gave them, Aldebaran, Betelgeuse, Rigel, Vega. They built the finest hospitals on Earth, with wards, pharmacies, and teaching, and they insisted, in an age of dogma, on a principle that would one day become the engine of everything: that a claim must answer to evidence and reason, and not merely to the authority of the ancients or the powerful.

The ethos was captured in a saying attributed to the Prophet himself, that one should seek knowledge even as far as China, and in another that the ink of the scholar is more sacred than the blood of the martyr. For several centuries, an enormous swath of the world took that seriously, from Córdoba in Spain, whose libraries dwarfed anything in Christian Europe and whose streets were lit at night, to Samarkand in Central Asia, where the astronomer-prince Ulugh Beg would later build a giant observatory and measure the length of the year to within seconds. The lamp of Alexandria, which we watched gutter and go out in the last Part, had not been extinguished after all. It had been carried east, and set burning brighter than it ever had before.

Why that light eventually dimmed is a genuine and much-debated question, and we will not pretend to a simple answer, because the honest one is contested. Part of it was catastrophe from outside: in 1258 the Mongols sacked Baghdad and, it is said, threw the books of the House of Wisdom into the Tigris until the river ran black with their ink, one of the great losses in the history of knowledge. Part of it, some historians argue, was a slow turn inward, a hardening of religious orthodoxy against the free philosophical speculation that had powered the golden age, though other scholars push back hard on that story as too simple and too convenient. What is not in doubt is the achievement itself, and its debt. When learning revived in Europe, it revived in large part by translating back out of Arabic the very Greek knowledge the Arabs had saved, along with everything the Muslim scholars had added to it. The West's own Renaissance had an Arabic-speaking parent it has too often forgotten to thank. And Islam was only one of the great lights of this supposedly dark age. There were others, and we turn next to a continent the old story dismissed most completely of all.