Between the 2nd century BC and the 2nd century AD, the Han dynasty developed an integrated system for producing high-carbon steel based on iron blast furnaces (生鐵, shēng tiě, 'living iron') followed by controlled decarburization through repeated forging to obtain high-strength malleable steel. The process required reaching temperatures above 1,200°C in forced-draft furnaces with mechanical bellows — archaeologically documented at the Guxingzhen (Henan) and Tieshengguo (Henan) sites — capable of fully melting iron, something European smiths would not achieve until the 14th century AD with the medieval blast furnace. The resulting steel (百煉鋼, 'hundred-times-forged steel') was distributed by the Han state as a strategic material; steel agricultural tools and weapons were a decisive factor in the expansion of the Han Empire. Large-scale cast-iron production is independent of the wootz crucible process of South India; the two represent distinct solutions to the same metallurgical problem. Europe did not develop cast-iron blast furnaces until c. 1150 AD in Sweden and the Rhineland, approximately 1,350 years after Han China.