Hülegü, sent west by his brother the Great Khan Möngke, besieged Baghdad in January 1258; the city surrendered on 10 February and was given over to a week or more of killing and plunder. The caliph al-Musta'sim was executed, reportedly rolled in a carpet and trampled to avoid spilling royal blood, ending five centuries of Abbasid caliphate. Figures for the dead vary wildly across the sources: Hülegü's own report to Louis IX gives about two hundred thousand, later Persian writers such as Wassaf give two million, and the intermediate tradition often gives eight hundred thousand. Modern assessments, including John Masson Smith's work on Mongol logistics, put the plausible toll far lower, in the tens of thousands to low hundreds of thousands, constrained by estimates of the city's population and the practicalities of killing over a limited period. Recent work in Medical History has also reassessed whether epidemic disease, rather than the sack alone, accounts for part of the mortality reported in the sources. The destruction of Baghdad's libraries is widely reported but its extent is debated.
Hülegü's Mongol army besieged and stormed Baghdad, executed the last Abbasid caliph al-Musta'sim, and killed or dispersed much of the city's population
Medieval chroniclers give death tolls from 200,000 to 2 million, figures modern historians reject as impossible. Estimates of the city's actual population in 1258, based on its built area and its long decline from the ninth-century Abbasid peak, cluster between about 250,000 and 400,000.
The low end reflects modern minimalist estimates constrained by the city's plausible population and the logistics of the sack; the high end is the figure most commonly transmitted in the Arabic and Persian tradition. Hülegü's own dispatch claimed about 200,000 and Wassaf claimed two million; neither is a count. Recent work has argued that epidemic disease may account for part of the mortality attributed to the sack.
The killing of the population, the plunder and burning of the city and the destruction of libraries and mosques are documented by Rashid al-Din, Ibn al-Fuwati, Bar Hebraeus and the Armenian chronicler Grigor of Akner, though the extent of the library destruction is disputed.
Iraq, Syria