 According Juvayni, Hulagu Khan brought with him 3,000 giant crossbows from China, for the siege of Nishapur, and a team of Chinese technicians to work a great 'ox bow' shooting large bolts a distance of 2,500 paces, which was used at the siege of Maymun Diz.According to the "Wujing Zongyao", these weapons had a range of 450 meters while other Song sources give ranges of more than double or even triple that.Constructing these weapons, especially the casting of the large triggers, and their operation required the highest order of technical expertise available at the time.