In 1221, Mongols led by Tolui attacked Merv, which surrendered after a seven-day siege. Upon the city’s surrender, the Mongols massacred the city’s inhabitants and enslaved around four hundred artisans and a number of children. Arab historian Ali ibn al-Athir states that 700,000 people were killed during the Mongol sack of Merv. The Mongols burned most of the city’s buildings, including the Tomb of Ahmad Sanjar. According to ibn al-Athir, the Mongols “set fire to the city and burned down the mausoleum of Sultan Sanjar, having dug up his grave in the search of precious objects.”' The fire caused significant damage to the structure, destroying much of the mausoleum’s exterior brickwork and causing the building’s outer dome to collapse. Merv remained severely depopulated in the period following the Mongol invasion and the tomb deteriorated further due to centuries of neglect.