The siege of Samarkand took place in March 1220 after Genghis Khan, founder of the Mongol Empire, had launched a multi-pronged invasion of the Khwarazmian Empire, ruled by Shah Muhammad II. The Mongols had laid siege to the border town of Otrar, but finding its defences obdurate, a large force commanded by Genghis and his youngest son Tolui detached from the vanguard and set off southwards, towards Transoxiana.
Samarkand was the Shah's capital and the pivot of his defence — the city's garrison was large and its battlements were one of the strongest in the empire. Genghis, however, managed to isolate it by capturing and destroying Bukhara in a surprise manoeuvre, and then laying waste to the nearby Transoxianan towns. After repelling relief forces, the Mongol army, now reinforced after the capture of Otrar, ambushed and massacred a sortie by the town's defenders. The citizens of the city soon surrendered at the instigation of the Muslim clergy; most were however enslaved or conscripted in traditional Mongol fashion.