Josef W. Meri (2005). Josef W. Meri, ed. Medieval Islamic Civilization: An Encyclopedia. Psychology Press. p. 510. ISBN0-415-96690-6. Consultado el 28 de noviembre de 2011. «This called for the employment of engineers to engaged in mining operations, to build siege engines and artillery, and to concoct and use incendiary and explosive devices. For instance, Hulagu, who led Mongol forces into the Middle East during the second wave of the invasions in 1250, had with him a thousand squads of engineers, evidently of north Chinese (or perhaps Khitan) provenance.»
Josef W. Meri; Jere L. Bacharach (2006). Josef W. Meri, Jere L. Bacharach, ed. Medieval Islamic Civilization: L-Z, index. Volume 2 of Medieval Islamic Civilization: An Encyclopedia (illustrated edición). Taylor & Francis. p. 510. ISBN0-415-96692-2. Consultado el 28 de noviembre de 2011. «This called for the employment of engineers to engaged in mining operations, to build siege engines and artillery, and to concoct and use incendiary and explosive devices. For instance, Hulagu, who led Mongol forces into the Middle East during the second wave of the invasions in 1250, had with him a thousand squads of engineers, evidently of north Chinese (or perhaps Khitan) provenance.»
h-net.org
Wei-chieh Tsai. Review of May, Timothy, The Mongol Conquests in World History H-War, H-Net Reviews. September, 2012. online