13 世纪，宋、蒙（元）双方出于战争需要，在川渝地区依山就水修筑了大批山地城防设施。近年来在重庆地区的南宋山城遗址——合川钓鱼城遗址和奉节白帝城遗址的大规模考古发掘中，都出土了一种特殊的爆炸性火器——火雷。这种火雷有铁质和陶质两类，铁火雷又有大小几种形制；陶火雷出土较少，现仅见于白帝城遗址。此外，白帝城遗址中还发现了与火雷冶铸有关的窑址和陶范，说明火雷可能为本地生产。重庆地区出土的这批南宋火雷是火药及火器演进史上最直接的证据，在军事技术史及科学技术史上具有非同凡响的意义。

The military situation of the thirteenth century required that the Song and the Mongols construct a great number of defensive works, relying on the mountains or facing the rivers, in the mountainous Sichuan Province and Chongqing. In recent years, a special kind of explosive firearms, huolei 火雷 (bombs), was unearthed in the large-scale excavations of the site of Diaoyu Fortress 钓鱼城 in Hechuan District 合川 and the Baidicheng 白帝城 in Fengjie County 奉节, both of which were defensive works constructed in this mountainous area during the Southern Song dynasty. In addition, the ruins of kilns and the clay molds that were relevant to the casting of iron huolei have been discovered at the site of Baidicheng, indicating that these huolei might have been produced locally. The Southern Song iron huolei unearthed in Chongqing are the most direct evidence of the evolvement of gunpowder and firearms, and are of great significance to the history of science and technology, in particular the history of military technology.