L. Carrington Goodrich (2002). A Short History of the Chinese People (illustrated utg.). Courier Dover Publications. s. 173. ISBN0-486-42488-X. Besøkt 28. november 2011. «In the campaigns waged in western Asia (1253-1258) by Jenghis' grandson Hulagu, "a thousand engineers from China had to get themselves ready to serve the catapults, and to be able to cast inflammable substances." One of Hulagu's principal generals in his successful attack against the caliphate of Baghdad was Chinese.»
