Baghdad in 1257 was still regarded as one of the great centres of Islam. The seat of the Abbasid caliphate, it was to an extent living on past glories, for its halcyon days were in the late eighth and early ninth centuries. Al-Mansur, the second caliph (reigned 754–775) and the real founder of the Abbasid dynasty, had laid the groundwork, but the great wonders came under Harun al-Rashid (ruled 786–809), the fifth caliph. He made Baghdad a showpiece of the world, with mosques, palaces, hospitals and irrigation works that astonished visitors and won him eternal fame.

Perhaps the most famous building of all was the House of Wisdom, the world’s largest library – also a research institute and translation centre. The House of Wisdom contained volumes and professors particularly specialising in the sciences: astronomy, mathematics, medicine, alchemy, chemistry, zoology, geography, cartography. But this was no mere Los Alamos or MIT of its day; the rigour and erudition of the institute was counterpointed by the colourful city of bazaars and markets outside where snake-charmers, fortune-tellers and hucksters of all kinds throve. Harun al-Rashid’s Baghdad, in short, was the one so unforgettably portrayed in the 1001 Nights. Under Harun and his immediate successors, Baghdad overtook Cordoba as the largest city in the world, but by the thirteenth century it had long since ceded the palm in the population stakes to Merv and the other great cities of Khorasan.