Baghdad has not figured so prominently in the news since the days when the caliph Harun al-Rashid earned his place in the Arabian Nights and Sinbad the Sailor flew to safety on a giant roc. That was 1,200 years ago, and today’s city is no longer a place where Neo-Platonist philosophers lock horns with Islamic theologians and palace ladies eat off jewel-studded golden platters. But Baghdad in the age of the Abbasid caliphs was the greatest of all cities, the political and military heart of the Islamic Empire at its height. Between its founding in A.D.762 and its destruction in 1258, the city was home to a huge advance in the breadth of human knowledge, so that it is remembered today not only as a place of pomp and luxury but as a city of scholarship and philosophy. Endowed with hospitals and mosques, adorned with palaces and gardens, the Baghdad of the Arabian Nights was a site of translation and transformation.

The second Abbasid caliph, al-Mansur, chose to create Baghdad on the middle reaches of the Tigris River, whence a dense network of canals stretched the 30 miles to the Euphrates River. He was consciously founding a new dynasty to replace the old Umayyad caliphs of Damascus, whose authoritarian rule had led to their recent downfall, and he had taken great care in selecting the site for the city. Ten thousand years before, farming had begun on the lands between the two rivers, and there in the heartlands of old Sumer, the first cities, Ur and Ctesiphon, Babylon and Agade, had risen and decayed, littering the region with their remains and bequeathing it an intricate web of irrigation canals. The land was level, productive, and cheap. ‘This,” said al-Mansur, “is an excellent place for a military camp,” and in 762 he laid the first brick with his own hands. For the next four years, architects, carpenters, masons, smiths, and construction workers, said to have numbered 100,000, labored to turn his plan into reality. The cost—4,883,000 dirhams—was scrupulously noted by the small army of accountants whose existence was a significant feature of the Abbasid regime.

The old imperial capital, Damascus, had been a city of the desert, surrounded by Arab tribes, but Baghdad lay like a hinge between the Semitic world of the Middle East and the Turkic and Perso-Indian lands beyond, reflecting the shifting center of Islamic gravity toward central Asia. The Arabs had made repeated efforts to conquer Constantinople, center of Byzantine Christendom, but the Abbasids largely turned from the Byzantine borders. Though Arabic remained the language of the state, the new capital was less obviously an Arab city, for Islam itself had outgrown its purely Arabic origins. Baghdad mirrored the growth of the new, multiracial Islam, shot through with influences from India, Alexandria, and, above all, Persia itself. Even among the caliphs, the Arab blood thinned from generation to generation. Instead of the old, rigid, tribal divisions, with their aristocracy of blood and book, pen and sword, the caliph ruled over a new class of men who lived by their wits. If Baghdad was a city of scholars, it was a city of businessmen, craftsmen, and merchants, too.

Baghdad stood for a new kind of imperial, Islamic unity that transcended the old racial connection between the Arabs and their faith to embrace people of many different races and backgrounds. As the home of the caliph, it was to be the center of a world that would be incorporated by degrees into the dar ul-Islam, the Realm of Peace, for which the city was first and officially named. Perhaps it was to express the notion that Baghdad stood as the point around which all the world revolved that al-Mansur first laid out his plan for the city in ashes, and revealed it to be a perfect circle.

The Round City, few traces of which remain, was a company town 1,000 cubits (about 500 yards) in diameter—a moated, gated, crenellated bastion of government, a bunker for the high command. The merchants were soon expelled beyond its walls, and the palaces of the empire’s grandees crept closer to the Tigris. At the city’s core lay the mosque and the first palace, known as the Golden Gate, which captured the popular imagination. Its halls were roofed in soaring domes, the largest of which was green and 130 feet high. The city walls were 40 feet wide and 90 feet high, with ramps for horsemen to reach the top; they were quartered precisely by gates high enough to let a lancer pass through without lowering his lance, and secured by gates of iron so heavy that a company of doormen was required to open and close each of them.

Almost everyone in Baghdad was on the caliph’s payroll—army men, members of the imperial family, and officials—and on their salaries the city spread rapidly. It grew toward the Tigris, incorporating the irrigation canals, throwing up palaces, mosques, bazaars, and houses for the common people. The Round City became, over the years, a city within a city, a citadel. As Baghdad grew, it ceased to be merely a bureaucratic capital and center of military power and became a city of extravagant fortune, linked to the ends of the earth by land and sea. It took rice, wheat, and linen from Egypt, glass from Lebanon, fruits from Syria, weapons and pearls from Arabia, minerals and dyes from India, perfumes and rugs from Persia, silk and musk from China, slaves from Africa and central Asia. It is still remembered as the home of that mythic traveler and trader, Sinbad the Sailor, whose story first appears in the pages of that quintessential product of Baghdad, the Arabian Nights.

Baghdad was a party town, and some of the most sumptuous entertainments were laid on by the Barmakids, a family whose name became synonymous with openhanded generosity. Under the new office of vizier, a position the Barmakids monopolized for three generations, the Abbasids established a powerful bureaucratic elite to supervise the gathering of taxes and revenues. Highly literate and urbane, these officials were frequently men of Persian origin who wrote and spoke in Arabic, the language of the state and the Quran. Under the Barmakids’ patronage, elements of Iranian thought and literature were drawn into the Islamic mainstream. The Barmakids grew fabulously rich and entertained their friends and allies in grand palaces constructed on the eastern side of the capital. They endowed mosques and built canals and established a kind of arts council to reward poets. But in 803 the Barmakids’ happy reign came to a sudden—and unexplained—end. The vizier’s head was struck off and his body cut in two, and the parts were displayed for a year on the city bridges.

Power, after all, lay with a single family, and it was the fourth and most famous of the Abbasid caliphs, Harun al-Rashid (ruler from 786 to 809), who set the Baghdad style. The marriage of his son al-Ma’mun to the daughter of a governor, for example, was marked by a party at which ambergris candles lit the palace, the couple sat on a golden mat studded with sapphires, and everyone of distinction received, as a going-home present, a ball of musk in which was tucked the deed to a valuable piece of land or to a slave.

But Baghdad’s contribution to history went well beyond the frivolity inspired by huge wealth. The rapid growth of the Islamic Empire brought Muslims into contact with peoples of other faiths and traditions whose intellectual culture was more refined and who presented a lively challenge to Islamic orthodoxy. Under the patronage of Harun and his son al-Ma’mun, the scholars drawn to the city began to release some of the intellectual currents of the ancient world into the mainstream of Islamic thought. Just as Baghdad was an entrepôt for the world’s goods, so it became a clearing-house for the higher sciences of mathematics, astronomy, medicine, law, and astrology.

In Baghdad, three of the four schools of Islamic jurisprudence were established, Arabic numerals (which the Arabs, more correctly, call Hindi numerals) were adopted, and zero, that elusive concept so vital to mathematical calculation, was probably invented. Under the great Persian physician al-Razi, Baghdad’s hospital set new standards for hygiene. The Muslims also took to philosophy. Al-Kindi, the first and perhaps the greatest Arab Neo-Platonist philosopher, served as a tutor to al-Ma’mun’s son and heir. He was a mathematician and a physician, a musician and an astrologer, who wrote dozens of books on subjects as varied as optics and health and once used music to cure a neighbor’s paralysis. In an effort to synthesize Platonic and Quranic explanations of the world, he fell back on the idea that truth was double edged: A simple religious truth brought comfort to ordinary people, and a higher, interpretive truth was vouchsafed to the learned. As one of his successors, Avicenna, remarked, “Religious law makes it illegal for the ignorant to drink wine, but intelligence makes it legal for the intellectual.”

In Baghdad, Syrian scholars with a profound knowledge of Greek oversaw the translation of most of the treasures of ancient science. If not for the scholars, those treasures would certainly have been lost. Ptolemy’s work on astronomy, translated into Arabic in 829 by a member of a pagan Syrian sect that worshiped the stars, became the Almagest; it survived in Arabic long after the Greek original had disappeared and laid down the structure of astronomy up to the time of Copernicus. The works of Euclid and Archimedes, Galen the herbalist, Hippocrates the doctor, and the philosophers Plato and Aristotle became known in translation to the Arab world centuries before they filtered to the West through Muslim Spain.

One newfangled doctrine of the period held that although the Quran was the word of God, it had been created in time and was not coeternal with him—a position suggesting that the Quran might be reinterpreted, even modified, for a new age. The later Abbasids embraced this doctrine, which allowed them considerable room for maneuver. But their religious heterodoxy added to the discontents that were already roiling the caliphate. In 836, during al-Mu’tasim’s reign, the Abbasids abandoned Baghdad for a new capital at Samarra, 80 miles to the north, under the protection of an army of Turkic horsemen recruited from the steppes. In Baghdad itself, opposition to the regime was marked by the renewed veneration of Muhammad (d. 632) and a barrage of scholarly inquiry into the hadith, a compendium of his doings and sayings. Sunni orthodoxy developed out of this reaction.

The caliphs returned to Baghdad some six decades years later, after years of factional fighting and civil war had severely weakened the machinery of the state and damaged the intricate irrigation systems on which the region’s prosperity depended. Unable to match their revenues to their expenditures, the caliphs were forced to give away more and more rights and lands to the distant rulers who were nominally under their dominion. The breakup of the empire across the Muslim world was mirrored locally by the rise of warlords such as ibn-Ra’iq, who in 936 was handed complete control of Baghdad and invited to take over the administration of the empire.

The caliphate became the pawn of powerful military adventurers who reduced the Abbasids to figureheads, and the rich lands around the city fell into relative decay. Spain had slipped from Baghdad’s control as early as 756, central Asia went after 820, and Egypt was lost to the rival Fatimid dynasty in 909. A century and a half after the founding of Baghdad, the basis for a single Islamic empire under Arab rule had disappeared. Baghdad itself became storied: The legendary generosity of the Barmakids, the luxury of the Golden Gate, the rovings of Sinbad, the wisdom of Harun al-Rashid, the tales of the philosophers, all passed, almost in a twinkling, into the realm of memory and myth.

In 1258, a huge Mongol army out of the steppe, drilled in the ways of victory and pitilessness, massed before the city gates. Baghdad was already out of shape. “This old city,” wrote the Andalusian traveler ibn-Jubayr in 1184, “still serves as the Abbasid capital . . . but most of its substance is gone. Only the name remains. . . . The city is but a trace of a vanished encampment, a shadow of a passing ghost.” The legacy of Baghdad’s science, translations, philosophy, and religious teachings had been spread from Spain to the borders of China, and its military genius had been transmitted to the Turks, who eventually spawned the empire of the Ottomans and carried Islam not only across the walls of Byzantium but deep into eastern Europe.

Genghis Khan and his Mongols had already swept through the old Islamic cities of Bukhara and Samarkand when his grandson Hulagu opened the siege of Baghdad. There was, it seems, no one in this great military camp left to defend it. The last Abbasid caliph offered an unconditional surrender, but Hulagu refused to hear him. A breach was opened in the walls on February 10, 1258, and Hulagu’s army poured into the defenseless city to slaughter everyone—the caliph and the Abbasid family, the court officials, the mullahs, and the people in the streets. The chronicles number the dead at 700,000. Libraries, houses, palaces, and mosques were set ablaze. Books that would not burn were thrown into the Tigris, whose water ran black for days. When the stench of death grew overpowering, the invaders, in classic Mongol fashion, removed themselves from the charred and ruined city—to return in the weeks that followed to cut down the survivors.

But the place continued to exist. Its shattered remains, and those who lived among them, were devastated again by Tamerlane in 1401, and for the next 500 years the town served as a minor provincial capital within the Ottoman Empire. A Frenchman who visited in 1651 drew a map of the ragged town that hardly differs from the maps the British prepared when they occupied it in 1917, but so utterly had Baghdad been forgotten in his day that the Frenchman called the place Babylon instead.