 Complete the following phrase:  Gunpowder weapons in the Song dynasty included fire arrows, gunpowder lit flamethrowers, soft shell bombs, hard shell iron bombs, fire lances, and possibly early cannons known as eruptors. The eruptors, such as the multiple bullets magazine eruptors bǎi-zi lián zhū pào, 百子連珠炮, consisting of a tube of bronze or cast iron that was filled with about 100 lead balls, and the flying-cloud thunderclap eruptor fēi yún pī-lì pào, 飛雲霹靂炮, were early cast-iron proto-cannons that did not include single shots that occluded the barrel thus called co-viative weapons. The use of proto-cannon, and other gunpowder weapons, enabled the Song dynasty to ward off its generally militarily superior enemiesthe Khitan led Liao, Tangut led Western Xia, and Jurchen led Jinuntil its 