The bone-rank system was the system of aristocratic rank used in the ancient Korean kingdom of Silla. It was used to segregate society, and particularly the layers of the aristocracy, on the basis of their hereditary proximity to the throne and the level of authority they were permitted to wield. The idea of royal blood in other societies is a close analogue to the idea of "sacred bone" in Silla thought. Bone rank was strictly hereditary, and thus acted as a caste system. The scholar, Lee Ki-Baik considers it to have probably been adopted as part of the administrative law introduced from China and promulgated by King Beopheung in 520. However, this likely did nothing but institute in legal fact what was already a society segregated by bloodline and lineage. Although only two of the five known ranks were referred to as "bone", the term "bone rank" has become widely used to describe the whole system. A person's bone rank status governed not only official status and marriage rights, but also the color of one's garments and the maximum dimensions of one's dwelling and carriage. These criteria are described in detail in the 12th century Korean historySamguk Sagi, particularly its Monographs, book 2. The Samguk Sagi's depiction of Silla life, however, has often been criticized for being excessively static. Unfortunately, since other sources are scarce, it is difficult to judge what sort of changes may have taken place in the bone rank system over the centuries.
Rank
Sacred Bone (Seonggol)
According to Samguk Sagi, "the people of Silla divided the period from Hyeokgeose of Silla to Jindeok of Silla into Sacred Bone, and the king after Muyeol of Silla into True Bone. The highest level of the bone rank was the "sacred bone", or seonggol, sometimes termed "hallowed bone". There is no specific record on exactly what the distinction between the Sacred Bone and the True Bone is set by, but is generally accepted that only the earliest kings were referred to as Seonggol. Because of this closed system of caste, when king Jinpyeong of Silla had no son whom he could pass the crown to, Queen Seondeok of Silla ascended the throne for the first time as a woman. And after that, Kim Chun-chu, also referred to as Muyeol of Silla ascended to the king as a Jingol status and since then, Jingol took over the throne for 281 years until Silla's demise.
True Bone (Jingol)
Below the sacred bone came the "true bone", or jingol. Members of the true bone could hold any official position, up to the level of full minister. They could also attain office rank up to the highest, ibolchan. After the sacred bone rank was abolished under King Muyol, only those holding the true bone rank could become king.
Head Ranks
Below the "true bone" came the head ranks, of which only the 6th, 5th and 4th are attested, 6th being the highest. The origins of these lower head rank classes and what defined one‘s status as such are obscure and still debated among scholars. As the jingol were prohibited from marrying into the lower ranks, though they could take concubines from them, it is feasible that one source of the head rank six were the children born from unions between jingol fathers and lower ranking concubines. In any case, members of the head rank six could rise to the position of vice-minister and as high as the 6th level of office rank, achan and sajung achan. Members of head ranks four and five could rise only to minor posts. Members of head rank five could reach the 10th level of office rank, daenaema, while members of head rank four could attain only the 12th level of office rank, daesa. There were 17 levels of office rank altogether. One scholar has proposed that, "head-ranks three, two, and one, if they ever formally existed, must have designated the... non-privileged general populace."
Evaluations
The frustrated ambitions of the head rank six class in particular seem to have played a prominent role in the politics of the late Silla period. Many men of head rank six status, proscribed from rising too high in the Silla administrative system defined by the bone rank system, sought to bypass this by studying Confucianismor else turned to careers in Buddhism. The most prominent of the head rank six figures was undoubtedly Choe Chiwon, who following an illustrious career in China returned to Silla only to see his attempts at administrative reform rebuffed by an entrenched aristocracy. In the early 10th century the nascent state of Goryeo, which succeeded Silla, tapped into the head rank six intellectuals to man its bureaucracy. The bone rank system's extreme rigidity certainly helped to weaken Silla toward the end of the Unified Silla period, although numerous other factors were at play. After the fall of Silla, the bone rank system was abolished entirely, although different and somewhat more flexible caste systems persisted until near the end of the Joseon Dynasty in the late 19th century.
