 Explosive shells had been in use in China for centuries but what was new was the counterweight type of trebuchet as opposed to the torsion type giving greater range and accuracy as it was easier to judge the weight of the counter weight than the torsion generated by repeated windings.The counterweight trebuchet built by the Muslims from Mosul were longer in range, and assisted in destroying Fancheng.Chinese and Muslim engineers operated Artillery and siege engines for the Mongol armies.