Baghdad is a city on the Tigris, founded by the Abbasid caliph al-Mansur in 762 CE and named by him Madinat al-Salam 1 2. The Turkish encyclopaedia of Islam calls it one of the important centres of history, learning and culture of the Islamic world and the seat of the caliphate from its foundation to the fall of the Abbasid state in 1258 CE, adding that the caliphs resided at Samarra from 836 to 892 CE 1 3. Al-Maqdisi relates that before building, al-Mansur asked about the site's winter and summer, rains and air, and had men sleep there through the seasons 4. He reports that al-Mansur summoned men learned in law and geometry, among them Abu Hanifa, had the city laid out and its foundations dug in 145 AH, and that it was finished in 149 AH 5.
Its core was a round city with a double wall and four gates, of Kufa, Basra, Khurasan and Syria, with the caliph's palace and the great mosque at its centre 2. Al-Mansur moved the treasury and the diwans there from Kufa in 146 AH/763 CE 2. Its markets were then moved to al-Karkh in 773 CE, and the city spread over both banks of the Tigris 6 2. The biography of al-Khwarizmi reports that an Indian astronomical text reached the court in Baghdad around 770 CE 7. In the book he completed in 375 AH, al-Maqdisi praised its "delicate air and subtle learning", and noted that Madinat al-Salam itself lay ruined in his day, its mosque still used on Fridays 8 9 4.
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