In terms of archaeological evidence, crossbow locks made of cast bronze have been found in China dating to around 650 BC. They have also been found in Tombs 3 and 12 at Qufu, Shandong, previously the capital of Lu, and date to the 6th century BC. Bronze crossbow bolts dating from the mid-5th century BC have been found at a Chu burial site in Yutaishan, Jiangling County, Hubei Province. Other early finds of crossbows were discovered in Tomb 138 at Saobatang, Hunan Province, and date to the mid-4th century BC. It is possible that these early crossbows used spherical pellets for ammunition. A Western-Han mathematician and music theorist, Jing Fang (78–37 BC), compared the moon to the shape of a round crossbow bullet. The "Zhuangzi" also mentions crossbow bullets.