This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Hulegu Khan's Mongol army besieged and took Baghdad between late January and 10 February 1258, ending five centuries of Abbasid rule as the caliphate's own political center in the city. Caliph al-Musta'sim surrendered and was executed ten days later, reportedly trampled by horses so as to avoid the Mongol taboo against spilling royal blood, and the city's palaces, libraries and centres of learning were sacked in the days that followed.
Later accounts that the Tigris ran black with the ink of destroyed manuscripts belong to tradition rather than to independently verified record, and modern historians note that Baghdad's great libraries had in fact reopened within two years of the siege. What did not survive was the Abbasid caliphate's own political power, the institutional heart of the Islamic Golden Age, which the siege ended even as the city itself and much of its scholarly life recovered.
What this changed for Islam's spread was the end of a single recognized political center for the Abbasid caliphate, which had stood in Baghdad for five centuries. Baghdad's libraries and learning survived the sack better than its rulers did, but the caliphate's own authority as a unified political institution did not outlast Hulegu Khan's army, and Islamic civilization afterward developed without the caliphal center that had anchored it since the eighth century.