My travels through Afghanistan in 1976 took me to Bamiyan. As evening was coming on, the bus from Kabul descended into the valley and dropped us at an inn. Early the following morning, I headed out to see the cliff face where two giant Buddhas stood until Taliban demolitionists dynamited them in 2001. Later that day, I walked to the hill at the head of the valley, a vast crowded mound of ancient rubble. Two broken brick towers were the only signs that a great city had once stood there. Its name, Shahr-e Gholghola (‘City of Cries’), caught a sense of what it must have been like on the day in 1221 when a Mongol army seized the city and levelled it.

What were the Mongols doing in Afghanistan in 1221? Mopping up. The year before, Genghis Khan had sent Jochi, the eldest of his four sons by his first wife, Börte, on a westward campaign that launched the family’s bid to rule not just the Mongols and their immediate vassals but