The House of Wisdom Read online

  Such problems of religious practice were addressed with relative ease by the early believers, grouped in a few communities in and around the Arabian Peninsula. For the most part, the ways of Muslim folk astronomy—based on visual cues and lacking the scientific astronomers’ theoretical basis—were sufficient. This was particularly the case in the regulation of the prescribed daily devotions, often denoted by the changing shadows cast by a special stick, called a gnomon, inserted into the ground or built into a sundial. The present-day definition of the prayer times dates back to the eighth century, with each to be completed within a certain period as marked by astronomical signs. The daytime devotions are defined by the length of the shadows, while those at night are tied to observable celestial events. The first prayer is said after sunset, the traditional start of the Muslim day, and must be completed before nightfall. The second is recited after nightfall, while the third is completed shortly before sunrise. The fourth, commonly known in the West as the noon prayer, actually begins when the sun has already begun its decline from the meridian, directly overhead. The final, afternoon prayer is also marked by the progression of the shadow and must be finished before the sun goes down, marking the end of one day and the beginning of the next.9

  Early Muslim scholars immediately grasped the importance of grounding their research in the faith, and many devoted the opening passages of treatises, commentaries, and other highly technical works to asserting the importance of their science to the daily concerns of the pious. This same concentration on practical issues may have left them vulnerable at times to conservative backlash. Once such problems were solved to the satisfaction of the believers, Muslim science would need to find new justifications for further study.10 But for now, faith and reason made for provocative bedfellows.

  The rapid spread of Islam across much of the known world that followed in the years after Muhammad’s death began to put the accurate determination of time, date, and direction out of reach of basic folk astronomy. By the time of the Abbasid Empire, the Muslim seafarer off the Chinese coast, the Arab merchant in faraway Spain, the pious believer in remote Central Asia—all required information that was increasingly hard to communicate from a distant central authority. The desire to observe religious obligations uniformly across the great expanse of Muslim territory mirrored the unanswered plea from Emperor Constantine four centuries earlier for all of Christendom to agree on a single recognized date to celebrate Easter. It also neatly complemented the intellectual ferment induced by the policies of the Abbasid court. Under the patronage of the early caliphs, the demands of religion and the imperatives of science were free to interact for centuries in ways unimaginable in medieval Europe. They also created ample scope for early work on fundamental scientific principles. Invaluable spin-offs included breakthroughs in geography, instrumentation, optics, and navigation.

  At first the muezzin, the town crier to daily prayer, was selected for his upstanding character and strong voice with which to summon the faithful from the top of the minaret. Over time, knowledge of the heavens was added to the list of requirements. “Only an honorable, reliable, and trustworthy man who is acquainted with the times of prayer may pronounce the call to prayer from the minaret … The muezzin must know the [twenty-eight] lunar mansions and the shapes of the star groups in them, so that he may be able to tell time at night,” advises the Egyptian commentator Ibn al-Ukhuwwa.11 In urban areas, the rise of the mosque-based timekeeper, a sort of holy astronomer, gradually displaced the older folk customs. These professional scientists regulated local prayer times, but they also built astronomical instruments, wrote treatises on spherical astronomy, and taught students. Their work included the production and publication of meticulous almanacs—from the Arabic al-manakh—that listed the prayer times for each day of the year in such distant locales as China and Morocco. In medieval Cairo, a leading center of such activity, some two hundred pages of special tables were available for keeping time by the sun and other celestial markers.

  Perhaps nowhere was the interaction of faith and science more important than in the question of the qibla, seen in the careful arrangements in all mosques to orient the believer. The earliest Muslims of Central Asia and Spain simply directed their prayers to the south, in imitation of the Prophet Muhammad when he was in Medina, 270 miles to the north of the holy city and the Kaaba. As the Arabs’ understanding of their universe became more sophisticated, they naturally demanded greater accuracy in conforming their practice to the sacred geography of Islam. “The Kaaba with respect to the inhabitants of the world is like the center of a circle with respect to the circle. All regions face the Kaaba, surrounding it as a circle surrounds the center, and each region faces a particular part of the Kaaba,” writes the twelfth-century religious jurist Zayn al-Din al-Dimyati.12 But where, exactly, was Mecca?

  One common approach invoked pre-Islamic Arabian directional systems of the four winds—the word qibla itself may derive from the traditional name of the prevailing easterly wind, qabul13—while others relied on the positions of prominent stars, the direction of the winter sunrise, or other easily observed phenomena. Another popular schema identified the four corners of the Kaaba with each of Mecca’s traditional regional trading partners: Syria, Iraq, Yemen, and “the West.” Thus, sacred geography easily complemented established practical systems used for centuries by the Arabs’ desert caravans and oceangoing merchant fleets as they followed traditional trade routes. Over time, finer distinctions were made by associating more narrow geographic zones with specific architectural features of the shrine, such as a waterspout or a doorway.14 A thirteenth-century Yemeni text, exquisitely titled The Sun, the Moon, and the Movements of the Fixed Stars Made Easy as a Gift to the Desirous and a Luxury for the Seeker, spells out a system of twelve geographic sectors centered on the Kaaba. Other versions featured as many as seventy-two divisions.15

  Such informal systems found favor with the Muslim jurists, who generally agreed that they met the requirements of the faith. But at times, confusion and conflict over the correct qibla prevailed. In one far-off land, for example, bewildered believers were faced with four different choices: One school of thought favored due west, in the direction of the traditional pilgrimage road to Mecca; another advocated the older, southern tradition of the Prophet at Medina; a third honored the qibla of the region’s earliest mosques; while a fourth preferred to leave the matter up to the astronomers.16 The use by the Muslims of earlier religious structures—such as synagogues or churches, with existing qiblas of their own—further complicated the picture. A mosque in the Negev Desert has been found with two different qiblas, one facing east toward Jerusalem and a later one, south toward the Kaaba.17 To this day, the prayer niches of many mosques fail to point the correct way to Mecca. This is particularly a problem in distant Indonesia, where lengths of string or other markers are commonly used to correct the qibla.18

  Understandably, such a state of affairs failed to satisfy the new breed of medieval Arab scientists, well versed in trigonometry, spherical geometry, and astronomy. One of the greatest Arab treatises on mathematical geography was a work by al-Biruni, written in the eleventh century, on finding the direction of Mecca from a city in Afghanistan.19The Determination of the Coordinates of Cities was the first in the history of the field to determine accurate geographic locales with the techniques of spherical trigonometry. His exacting approach was designed to replace the difficult and less reliable method then in widespread use for determining differences in longitude: the simultaneous observation of a lunar eclipse from two distinct points. Al-Biruni’s dedication to his science was so absolute, we are told, that “his hand scarcely ever left the scroll, nor his eyes ceased observing and his heart pondering except on the two … [Persian holidays], Nowruz and Mihragan.”20 While his work contains some minor errors, it was not surpassed in any meaningful way until the nineteenth and even twentieth centuries.21 For the likes of al-Khwarizmi, al-Biruni, and their empirically minded colleagues, the huge expanse
of the Arab empire also fueled the arts of mapmaking and navigation, drove the development of portable scientific instruments such as the astrolabe, and created scope for major advances in many other disciplines that would later prove essential to Western science.

  Astronomy and related disciplines were not the only beneficiaries of Islam’s flush of enthusiasm for learning. Magic, experimentation, and science all came together in the form of al-kimia, the cornerstone of modern chemistry. Controversy over whether it was acceptable in theological terms to depict man and animals in art led to the heavy use of precise, stylized decoration for public structures, ceramics, and textiles that captured the Muslims’ highly developed understanding of geometry. A mathematical study in 2007 found that medieval Muslim architects had worked out complex mosaic patterns using just five different shapes of tiles that could in theory form patterns that were infinitely large yet never repeated. One example from a fifteenth-century Muslim shrine in the Iranian city of Isfahan displays geometric patterns whose underlying mathematics was only understood in the West five hundred years later.22

  Koranic injunction on the need to heal the sick, meanwhile, spurred enormous gains in medicine and the creation of advanced hospitals, complete with such innovations as specialized wards, regular doctors’ rounds, free health care for indigent patients, and humane treatment of the insane. Grounding their work in Greek learning initially passed along by Nestorian Christians fleeing Byzantine religious persecution, the Arabs went on to develop new medicines and new methods for preparing the active ingredients of these drugs. They made important discoveries in the field of vision and optics and advances in surgery. Revealing an early and growing recognition of germs and other disease pathways, the authorities chose to base Baghdad’s main hospital at a site where tests had shown that raw meat putrefied most slowly.

  Major medical schools were established in Damascus, Baghdad, Cordoba, and Cairo. The Persian physician and philosopher Avicenna’s eleventh-century Canon of Medicine served as the leading medical text in the West for more than five hundred years, while the medical school at Salerno, in southern Italy, was a primary conduit conveying Muslim medical learning to Western Europe. Adelard of Bath visited Salerno during his grand tour, but there is no record that he ever delved into the healing arts. Unlike the medieval Christian West, which tended to view illness and disease as divine punishment, the Arab physicians looked for imbalances or other physical causes that could be treated as part of their religious mission.

  Islam also places a premium on personal hygiene, a fact underscored by the ritual washing of the hands, feet, and face before each of the five daily prayers. Many medieval mosques and other public buildings featured sophisticated water-delivery systems, a field in which early Arab engineers excelled. Among the innovations they pioneered were elaborate feedback mechanisms and automatic controls to regulate machinery without human intervention. Other developments included the twin-cylinder pump with true suction and the crankshaft, for the efficient transmission of power. The latter did not begin to appear in European machines until the fourteenth century.23 A treatise from 1206 by the greatest of the medieval engineers, Ibn al-Razzaz al-Jazari, discusses water clocks and candle clocks, wine dispensers, sophisticated fountains, and musical automatons—most famously, a programmable drum machine consisting of four figures in a boat—as well as advanced systems for raising water from wells, cisterns, and the like. His descriptions are so accurate that they have been used in modern times to re-create some of his unique machines.24

  As the symbolic heir to the Prophet, Caliph al-Mamun was responsible—at least in theory—for the religious well-being of the vast community of believers. At the same time, he was the head of an enormous empire, with all the attendant political, economic, military, and administrative complexities. For help with both realms, the spiritual and the temporal, the caliph turned to the scholars at the House of Wisdom. Inquisitive by nature and well disposed toward science by upbringing, he called on these experts to determine the precise locations of Baghdad and Mecca in order to define the correct, religiously mandated qibla. Such information would also aid the hajj pilgrims, who were interested in the distance to Mecca, as well as the shortest route to the Kaaba, and assist in proper observation of the sacred lunar calendar. The latter was particularly tricky. Religious practice dated the start of the month to the first sighting of the new moon, requiring the astronomer to know the lunar orbit as well as the corresponding positions of the sun and the earth in order to predict “crescent visibility.” Like any self-respecting potentate, the Abbasid caliph also wanted an accurate portrayal of the length and breadth of the world now at his feet.

  For the astronomers and other scientists from the House of Wisdom, all of these matters could be reduced to fundamental problems of spherical geometry. With the help of the ancients, they had mastered the system of geographic coordinates—that is, the use of imaginary circles of longitude and latitude girding the earth to provide each point with a unique, identifiable location. Unlike medieval Christendom, Islam offered no resistance to the classical notion of the earth as a globe; from the start, Arab scholars readily applied the mathematics of the sphere to questions of geography. From Ptolemy, author of the Almagest and the almost equally influential Geography, these scientists learned of the problem of projection, the representation of the round surface of the earth on a flat, two-dimensional map. Al-Mamun’s geodetic survey in the desert plains of Sinjar had already yielded the length of one degree in Arabic units of measurement, while the Muslims’ corrections and additions to Ptolemy’s table of coordinates for eight thousand cities and other locales provided new, more accurate data for astronomers and geographers alike.

  Taken together, the information and techniques developed by al-Mamun’s experts and others like them—basically a matter of geometry and trigonometry applied to the sphere of the earth—could determine the qibla with remarkable accuracy from the local north-south meridian along the Great Circle of the earth’s globe. The tradition of sacred geography defined the qibla as a “commonsense” straight line between the believer and Mecca, but the mathematicians and astronomers of the House of Wisdom knew that the spherical shape of the earth meant that the true qibla was in reality a curved line at a specific angle from the point of prayer, known to this day by the term azimuth, from the Arabic al-sumut. This difference between the two approaches to the problem of the qibla became more pronounced as the distance from Mecca increased, and it was a measure of the influence of the mathematical astronomers that theirs was generally adopted as the consensus among believers. Such a system of Great Circle measurement lies at the foundation of modern-day calculations of geographic distance and direction.25 It also formed the basis for one of al-Mamun’s greatest scientific triumphs, the construction of a world map, with an accompanying description of the earth’s people, places, and wonders and an updated table of geographic coordinates to aid future research.

  Such efforts were not unknown in the early Muslim world. Al-Masudi tells us that two hundred years before al-Mamun’s day, the early Muslim authorities sought information on the expanding realm of Islam. “The custodians of the tradition say that when by Allah’s will the Muslims conquered the lands of Iraq, Syria, Egypt and other countries, [Caliph] Umar ibn al-Khattab wrote to one of the learned men of the age: ‘We are nomads, and Allah made us conquer these lands, and we want to settle in them and dwell there. Describe therefore to us the towns, their air, their position, how people are affected by the land and the air.’ ” According to al-Masudi, the sage responded with descriptions of Syria, Egypt, Iraq, and parts of Persia but deliberately omitted any word of India, China, or the West. “You do not need any description of them, for they are very far and out of the way, countries of unbelievers and tyrants.”26

  Al-Mamun and his researchers could also rely on some more technically proficient works, including early military maps and surveys and detailed accounts of the Muslim empire’s elaborate system of post roads, c
omplete with records of routes, distances, and travel times. Stone markers showing the distance from Baghdad have been found as far away as Palestine and Georgia, in Caucasia.27 The postmaster and head of intelligence in northwest Persia later compiled a famous survey of such data into The Book of Roads and Kingdoms. Merchants, sailors, spies, and postal authorities across the empire were ideal sources of information for the caliphs and their administrators back in the Abbasid capital. The Book of Roads and Kingdoms also includes major sea routes to Persia, Bahrain, Oman, and Yemen and beyond to Cambodia, the Malay Peninsula, and finally the harbor at Canton, China.28 Similar works in this vein later added a wealth of economic data, useful for trade, tax collection, and related imperial matters.

  Still, al-Mamun had far greater ambition for his world map and its account of human geography. He assembled a team of several dozen scholars. The scope of the project, says al-Masudi, included nothing less than “the universe with its spheres and stars, the land and the sea, inhabited and uninhabited parts, the populated areas of the peoples, cities and similar aspects.”29 A later account, by Abu Abdallah al-Zuhri, reports that along with prominent geographic features, the royal geographers of early ninth-century Baghdad included “what famous and marvelous things are to be found in individual parts of the earth and what historical monuments and edifices are to be found in the individual countries.”30 Among these “famous and marvelous things” was a geographically accurate description of the Great Wall of China.

  In addition to such curiosities, the Mamun map and survey depicted 530 important cities and towns, five seas, 290 rivers, and 200 mountains, nothing their estimated size and any deposits of metals or precious stones. These features were apportioned among the seven so-called climata, the traditional Greek division of the known world into equal parallel zones extending northward from the equator. This system had been introduced to the Arabs by Ptolemy, but the scholars of al-Mamun made some refinements, including the introduction of two new, barely inhabited zones just below the equator to conform to more up-to-date information at their disposal. They also revised the length of the Mediterranean, reducing Ptolemy’s measurement of sixty-two degrees of longitude to fifty-two degrees; this was later trimmed again in the early eleventh century by Arab geographers to forty-two degrees, very near to its modern value.31 Most important of all, the caliph’s scholars corrected Ptolemy’s traditional representation of the Indian Ocean as a landlocked sea and, for the first time, made it clear that a global body of water surrounds the inhabitable world32—a significant breakthrough in the history of cartography that prefigured by six hundred years the coming of Europe’s so-called Age of Discovery, beginning in the mid-fifteenth century.