In 1221 Merv opened its gates to Tolui, son of Genghis Khan, chief of the Mongols, on which occasion most of the inhabitants are said to have been butchered. The Persian historian Juvayni, writing a generation after the destruction of Merv, wrote
- “The Mongols ordered that, apart from four hundred artisans. .., the whole population, including the women and children, should be killed, and no one, whether woman or man, be spared. To each [Mongol soldier] was allotted the execution of three or four hundred Persians. So many had been killed by nightfall that the mountains became hillocks, and the plain was soaked with the blood of the mighty.”
Some historians believe that over one million people died in the aftermath of the city’s capture, including hundreds of thousands of refugees from elsewhere, making it one of the most bloody captures of a city in world history.
Excavations revealed drastic rebuilding of the city’s fortifications in the aftermath, but the prosperity of the city had passed. The Mongol invasion spelt the eclipse of Merv and indeed of other major centres for more than a century. After the Mongol conquest, Merv became part of the Ilkhanate and was consistently looted by Chagatai Khanate. In the early part of the 14th century the town became the seat of a Christian archbishopric of the Eastern Church under the rule of the Kartids, vassals of the Ilkhanids. By 1380 Merv belonged to the empire of Timur (Tamerlane).