 The Chinese scholar Zheng Sixiao (1206–83) indicates that, "in the case of the largest ones, the wooden framework stood above a hole in the ground".After Aju asked Kublai, the Emperor of the Mongol Empire, the powerful siege machines of the Ilkhanate, Ismail and Al-aud-Din from Iraq arrived in South China to construct a new type of trebuchet which used explosive shells.These Muslim engineers built mangonels and trebuchets for the siege.