Cast Iron (5th century BCE)

Cast iron emerged in 5th century BCE China as a decisive industrial breakthrough, with furnaces reaching 1,150°C—200°C hotter than those of any contemporary civilization. Chinese metallurgists produced up to 500 kilograms of cast iron per batch, a scale 40% larger than the average European foundry would achieve until the 14th century. This technology outperforms #4's bronze-casting techniques by enabling mass-production of plows and swords, directly fueling the Warring States' agricultural expansion.