Swords have a long history in China. Bronze swords have been traced back to the bronze daggers of the Shang dynasty. Bronze long swords suddenly appeared during the mid-third century BC. Later swords were made of iron or steel. These metals were wrought, never cast. Swords commonly reached a length of 70–100 cm, although longer swords have been found. Chinese iron swords were used in Japan from the third to sixth century AD, but were replaced with Korean and native Japanese swords by the middle of the Heian era.