Analysis of information sources in references of the Wikipedia article "Conquête mongole de l'empire des Song" in French language version.
« For his part Kublai dedicated himself totally to the task, but it was still to be the Mongol's toughest war. The Sung Chinese showed themselves to be the most resilient of foes. Southern China was not only densely populated and full of strongly walled cities. It was also a land of mountain ranges and wide fast-flowing »
« Unquestionably in the Chinese the Mongols encountered more stubborn opposition and better defense than any of their other opponents in Europe and Asia had shown. They needed every military artifice known at that time, for they had to fight in terrain that was difficult for their horses, in regions infested with diseases fatal to large numbers of their forces, and in boats to which they were not accustomed. »
« "zhen tian lei (or chen t'ien lei) (Chinese 'heaven-shaking thunder') medieval Chinese explosive bombs first used by the Jurchen Jin dynasty at the siege of the Song Chinese city of Qizhou in 1221… [Replacing bamboo enclosures,] the zhen tian lei had a cast-iron casing [that produced] a genuine fragmentation bomb. [They] were used by the Jin in defense of Kaifeng…, by the Song defenders of Xiangyang… and other cities, and in the Mongol invasions of Japan. They were launched from trebuchets, or even lowered on chains into besiegers approach trenches. The fragments pierced iron armor and the explosion could be heard 50 km / 31 miles away." »
« overthrown, as we shall see — since the final counter-offensive launched by the Chinese against their Mongol overlords of the Yuan dynasty is a story in which artillery features significantly. By 1259 at least, if not earlier during the first Mongol invasions, the Chinese were using tubes that shot bullets. The t'u huo ch'iang ("rushing- forth fire- gun") was a long bamboo tube into which bullets in the true sense (tzu-k'o) »
