Analysis of information sources in references of the Wikipedia article "Hulegu Khan" in English language version.
This called for the employment of engineers to engage 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.