The foundation of this legacy was the astonishing achievements of Muslim scholars, scientists, craftsmen, and traders during the two hundred years or so that are called the Golden Age. During this period, from 750 to 950, the territory of the Muslim Empire encompassed present-day Iran, Syria, Iraq, Egypt, Palestine, North Africa, Spain, and parts of Turkey and drew to Baghdad peoples of all those lands in an unparalleled cross-fertilization of once isolated intellectual traditions.

Geographical unity, however, was but one factor. Another was the development of Arabic, by the ninth century, into the language of international scholarship as well as the language of the Divine Truth. This was one of the most significant events in the history of ideas.

A third important factor was the establishment in Baghdad of a paper mill. The introduction of paper, replacing parchment and papyrus, was a pivotal advance which had effects on education and scholarship as far reaching as the invention of printing in the fifteenth century. It made it possible to put books within the reach of everyone.

Unlike the Byzantines, with their suspicion of classical science and philosophy, the Muslims were enjoined by the Prophet to "seek learning as far as China" - as, eventually, they did. In the eighth century, however, they had a more convenient source: the works of Greek scientists stored in libraries in Constantinople and other centers of the Byzantine empire. In the ninth century the Caliph al-Mamun, son of the famous Harun al-Rashid, began to tap that invaluable source. With the approval of the Byzantine emperor, he dispatched scholars to select and bring back to Baghdad Greek scientific manuscripts for translation into Arabic at Bayt al-Hikmah, "the House of Wisdom."

Bayt al-Hikmah was a remarkable assemblage of scholar-translators who undertook a Herculean task: to translate into Arabic all of what had survived of the philosophical and scientific tradition of the ancient world and incorporate it into the conceptual framework of Islam.

As the early scholars in the Islamic world agreed with Aristotle that mathematics was the basis of all science, the scholars of the House of Wisdom first focused on mathematics. Ishaq ibn Hunayn and Thabit ibn Qurrah, for example, prepared a critical edition of Euclid's Elements, while other scholars translated a commentary on Euclid originally written by a mathematician and inventor from Egypt, and still others translated at least eleven major works by Archimedes, including a treatise on the construction of a water clock. Other translations included a book On mathematical theory by Nichomachus of Gerasa, and works by mathematicians like Theodosius of Tripoli, Apollonius Pergacus, Theon, and Menelaus, all basic to the great age of Islamic mathematical speculation that followed.

The first great advance on the inherited mathematical tradition was the introduction of "Arabic" numerals, which actually originated in India and which simplified calculation of all sorts and made possible the development of algebra. Muhammad ibn Musa al-Khwaraznli seems to have been the first to explore their use systematically, and wrote the famous Kitab al-Jabr wa-l-Muqabalah, the first book on algebra, a name derived from the second word in his title. One of the basic meanings of jabr in Arabic is "bonesetting," and al-Khwarazmi used it as a graphic description of one of the two operations he uses for the solution of quadratic equations.

The scholars at Bayt al-Hikmah also contributed to geometry, a study recommended by Ibn Khaldun, the great North African historian, because "it enlightens the intelligence of the man who cultivates it and gives him the habit of thinking exactly." The men most responsible for encouraging the study of geometry were the sons of Musa ibn Shakir, al-Mamurl's court astronomer. Called Banu Musa - "the sons of Musa" - these three men, Muhammad, Ahmad, and al-Hasan, devoted their lives and fortunes to the quest for knowledge. They not only sponsored translations of Greek works, but wrote a series of important original studies of their own, one bearing the impressive title The Measurement of the Sphere, Trisection of the Angle, and Determination of Two Mean Proportionals to Form a Single Division between Two Given Quantities.

The Banu Musa also contributed works on celestial mechanics and the atom, helped with such practical projects as canal construction, and in addition recruited one of the greatest of the ninth-century scholars, Thabit ibn Qurrah.

During a trip to Byzantium in search of manuscripts, Muhammad ibn Musa happened to meet Thabit ibn Qurrah, then a money changer but also a scholar in Syriac, Greek, and Arabic. Impressed by Thabit's learning, Muhammad personally presented him to the caliph, who was in turn so impressed that he appointed Thabit court astrologer. As Thabit's knowledge of Greek and Syriac was unrivaled, he contributed enormously to the translation of Greek scientific writing and also produced some seventy original works - in mathematics, astronomy, astrology, ethics, mechanics, music, medicine, physics, philosophy, and the construction of scientific instruments.

Although the House of Wisdom originally concentrated on mathematics, it did not exclude other subjects. One of its most famous scholars was Hunayn ibn Ishaq, Ishaq's father - known to the West as Joanitius - who eventually translated the entire canon of Greek medical works into Arabic, including the Hippocratic oath. Later a director of the House of Wisdom, Hunayn also wrote at least twenty-nine original treatises of his own on medical topics, and a collection of ten essays on ophthalmology which covered, in systematic fashion, the anatomy and physiology of the eye and the treatment of various diseases which afflict vision. The first known medical work to include anatomical drawings, the book was translated into Latin and for centuries was the authoritative treatment of the subject in both Western and Eastern universities.

Others prominent in Islamic medicine were Yuhanna ibn Masawayh, a specialist in gynecology and the famous Abu Bakr Muhammad ibn Zakariya al-Razi - known to the West as Rhazes. According to a bibliography of his writings al-Razi wrote 184 works, including a huge compendium of his experiments, observations, and diagnoses with the title al-Hawi, "The All-Encompassing."

A fountainhead of medical wisdom during the Islamic era, al-Razi, according to one contemporary account, was also a fine teacher and a compassionate physician, who brought rations to the poor and provided nursing for them. He was also a man devoted to common sense, as the titles of two of his works suggest. The Reason Why Some Persons and the Common People Leave a Physician Even If He Is Clever, and A Clever Physician Does Not Have the Power to Heal All Diseases, for That is Not within the Realm of Possibility.

The scholars at the House of Wisdom, unlike their modern counterparts, did not "specialize." Al-Razi, for example, was a philosopher and a mathematician as well as a physician and al-Kindi, the first Muslim philosopher to use Aristotelian logic to support Islamic dogma, also wrote on logic, philosophy, geometry, calculation, arithmetic, music, and astronomy. Among his works were such titles as An Introduction to the Art of Music, The Reason Why Rain Rarely Falls in Certain Places, The Cause of Vertigo, and Crossbreeding the Dove.

Another major figure in the Islamic Golden Age was al-Farabi, who wrestled with many of the same philosophical problems as al-Kindi and wrote The Perfect City, which illustrates to what degree Islam had assimilated Greek ideas and then impressed them with its own indelible stamp. This work proposed that the ideal city be founded on moral and religious principles from which would flow the physical infrastructure. The Muslim legacy included advances in technology too. Ibn al-Haytham, for example, wrote The Book of Optics, in which he gives a detailed treatment of the anatomy of the eye, correctly deducing that the eye receives light from the object perceived and laying the foundation for modern photography. In the tenth century he proposed a plan to dam the Nile. It was by no means theoretical speculation; many of the dams, reservoirs, and aqueducts constructed at this time throughout the Islamic world still survive.

Photo: At Hama in Syria, antique wooden wheels still lift the waters of the Orontes to gardens, baths, and cooling fountains.

Muslim engineers also perfected the waterwheel and constructed elaborate underground water channels called qanats. Requiring a high degree of engineering skill, qanats were built some fifty feet underground with a very slight inclination over long distances to tap underground water and were provided with manholes so that they could be cleaned and repaired.

Agricultural advances are also part of the Muslim legacy. Important books were written on soil analysis, water, and what kinds of crops were suited to what soil. Because there was considerable interest in new varieties - for nutritive and medicinal purposes - many new plants were introduced: sorghum, for example, which had recently been discovered in Africa.

The introduction of numerous varieties of fruits and vegetables and other plants to the West via the Islamic empire was, however, largely the result of the vast expansion of trade during the Golden Age. This trade was vital; in the central lands of the 'Abbasid empire natural resources such as metals and wood were scarce, and increases in urban populations had outstripped the capacity of the agricultural system to support them. The 'Abbasids, therefore, were forced to develop extensive and complicated patterns of trade. To obtain food, for example, Baghdad had to import wheat from Syria and Egypt, rice from the Fayyum in Egypt, southern Morocco, and Spain, and olive oil from Tunisia. Called "a forest of olive trees," Tunisia exported so much olive oil that its port of Sfax was called "the port of oil."

To obtain scarce metals the 'Abbasids had to turn elsewhere. They imported the technologically advanced "ondanique" steel from India, for example, and then processed it at such famous centers of weapons manufacture as Damascus and Toledo, both of which cities won fame for their blades. The 'Abbasids also imported iron from Europe, tin from the British Isles and Malaya, and silver from northern Iran, Afghanistan, and the Caucuses. For gold, once the vast quantities in the treasuries of the conquered countries were exhausted, they turned to several sources. One was the gold mines of the Hijaz which were reopened around 750, reworked for about four hundred years, and then, in 1931, explored again by Karl Twitchell, who was searching for minerals in that area on behalf of King 'Abd al-'Aziz of Saudi Arabia.

For these necessities the 'Abbasid traders exchanged a wide variety of products: pearls, livestock, paper, sugar, and (a specialty of the Islamic world) luxurious cloth. The traditional cloths were wool and linen - the latter an Egyptian specialty since ancient times - but cotton, which was introduced into upper Iraq about the time of the Prophet, later spread with Islam around the Mediterranean, to Syria, North Africa, Spain, Sicily, Cyprus, and Crete.

The cloth trade produced a number of auxiliary exports: gold and silver thread for embroidery, gum from the Sudan for glazing, and needles, looms, and dyestuffs. Closely connected with the trade in dyestuffs was the trade in medicines, an offshoot of 'Abbasid advances in medicine and the spread of hospitals in all major Islamic cities. As scientific research and translation of medical texts from India and possibly even China expanded the earlier pharmacopoeia, ingredients for medicines were brought from all over the known world and also reexported.

Because the religious, political, and military achievements of the Islamic period loom so large in the history of the world, the extraordinary cultural, scientific, technological, and commercial achievements are frequently obscured or overlooked. Yet these advances were, in fact, of enduring significance to mankind as a whole. The destruction by the Mongols of many of these achievements and of much of what the Muslims had accomplished by the end of the Golden Age was a tragic loss for the world as a whole.

Architectural monuments spanning a thousand years bear witness to the spread of Islam.

Photo: Jerusalem's Dome of the Rock, built in 691-692.

Photo: Purity of line characterizes the late twelfth century Kutubiyah Mosque of the Berbers in Marrakesh.

Photo: Water courses and fountains make an oasis of the Alhambra palace built at Granada in the fourteenth century Here incredibly light and elegant elements of Islamic decoration find their highest realization.

Photo: Sixteenth century Sultan Selim Mosque at Edirne is the apogee of Ottoman Turkish architecture, soaring space enclosed with a massive dome.

Photo: Persia's greatest contribution to ornament, gloriously colored enameled tile, faces the dome and stalactite portal of Shaykh Lutf Allah Mosque, built in the early 1600s on Isfahan's vast royal plaza.

Photo: The peak of Mogul architecture and possibly the most famous work of all times and cultures is the dazzling Taj Mahal mausoleum built at Agra in 1629.