In 762 a caliph founded a round city on the Tigris and made it the capital of the world. For five centuries Baghdad was where the planet's knowledge was collected, translated, argued over, and improved — the House of Wisdom, where scholars were paid their weight in gold. More or less literally.
The empire in images
The rise
In 750 the Abbasids overthrew the Umayyads in a revolution that shifted Islam's center of gravity east — from Arab Syria to cosmopolitan Iraq. The new dynasty leaned on Persian administrators and Khorasani soldiers; the caliphate became less an Arab kingdom and more a universal empire, open to talent from every people it ruled.
Al-Mansur founded Baghdad in 762 — a perfectly round city, the City of Peace — positioned to catch the trade of three continents. Under Harun al-Rashid, who reigned 786 to 809 (the caliph of the Thousand and One Nights), and his son al-Ma'mun, who reigned 813 to 833, the court poured money into translation: Greek, Persian, and Indian works rendered into Arabic at the Bayt al-Hikma, the House of Wisdom.
The zenith
What happened there changed the world. Al-Khwarizmi wrote the book that gave us “algebra” (from al-jabr) and the Latinized name behind “algorithm.” Physicians like al-Razi ran bimaristans — hospitals with wards, pharmacies, and medical schools — centuries before Europe had anything comparable. Astronomers, opticians, chemists: Baghdad was doing science while Europe was doing penance.
The economy matched the intellect. Abbasid dinars circulated from Spain to China; paper mills — the technology learned from Chinese prisoners at Talas in 751 — made books cheap; Basra's merchants traded with India and East Africa. Baghdad at its height may have held a million people: the largest city west of Chang'an, and the richest.
The fall
The decline was slow, then sudden. Provincial governors became hereditary emirs; Turkish slave-soldiers became kingmakers; by the tenth century the caliph was a religious figurehead while Buyids, Seljuks, and Fatimids held real power. The empire fragmented — but Baghdad remained the symbolic heart of Sunni Islam, and the caliph's name was still prayed for from Spain to India.
The end came in 1258, when the Mongol Hulagu Khan sacked Baghdad. The Tigris ran black with ink from the libraries thrown into it — or so the chroniclers say, and for once the metaphor may not exaggerate the loss. The caliph was rolled in a carpet and trampled by horses. Five centuries of the Islamic golden age ended in a week.
The Abbasid legacy is the foundation under modern science: algebra, algorithms, the hospital as an institution, and the preservation — and extension — of Greek, Persian, and Indian knowledge that Europe would later re-import and call the Renaissance. Europe's great rebirth was, in large part, a translation project; the Abbasids had done the first draft.
And there is Baghdad itself: the eternal symbol of the Islamic golden age, the city of the Thousand and One Nights, the proof — still cited, still argued over — that Islamic civilization at its height led the world in reason and learning. For five hundred years, Arabic was the language of science. It could be again; that is the argument Baghdad makes, silently, to this day.