On certain restless nights, despite the plush furnishings of his royal bed or the soothing melodies of his musicians or even the exquisite attentions of one or more of his 300 concubines, the mighty caliph Harun al-Rashid, fifth in the Abbasid line, could not find sleep. Accompanied by his favourite eunuch, Masrur, who also served as his headsman, he prowled the palace gardens or roamed in disguise through the souks of Baghdad; sometimes he summoned learned scholars for a chat – normally an infallible remedy for insomnia. If these expedients failed, he had his eunuch fetch Ali ibn Mansur, a wit from Damascus, to while away the long hours of the night with his fabulous tales. In the end, only stories could lull the caliph to sleep.

The sleepless Harun al-Rashid figures prominently, of course, in the vast compendium of bedtime stories we know as The Arabian Nights – Alf Layla wa-Layla in Arabic or The Thousand Nights and a Night. As the prolific scholar and novelist Marina Warner notes in her wonderful new study of the