The Bone-Rank System in the ancient Korean kingdom of Silla was a hereditary caste system used to segregate society, particularly the aristocracy, based on their proximity to the throne and level of authority. This system was likely influenced by administrative laws from China, instituted by King Beopheung in 520. The Samguk Sagi, a 12th-century Korean historical text, provides a detailed account of this system, including its influence on aspects of life such as official status, marriage rights, clothing, and living conditions, though its depiction of Silla society has been criticized for being excessively static.^[54]

The highest rank in the Bone-Rank System was the "sacred bone" (Seonggol), followed by the "true bone" (Jingol), with the king after Muyeol of Silla belonging to the latter category, marking a shift in the royal lineage for over 281 years until Silla's demise.^[55] Below the "true bone" were the head ranks, with only the 6th, 5th, and 4th ranks attested, and the origins and definitions of these lower ranks remaining a topic of scholarly debate. Members of the head rank six could attain significant positions within the administrative system, while those in ranks four and five were limited to minor posts. The rigidity of the Bone-Rank System, and the limitations it placed on individuals, particularly those of the head rank six class, played a significant role in the politics of late Silla, with many seeking opportunities in Confucianism or Buddhism as alternatives.

The Bone-Rank System’s rigidity contributed to the weakening of Silla towards the end of the Unified Silla period, despite other factors also being at play. Following Silla's fall, the system was completely abolished, though various caste systems persisted in Korea until the late 19th century. The frustrated ambitions of the head rank six class and their subsequent search for opportunities outside the traditional administrative system highlight the system’s restrictive nature and its impact on Korean society during this period.