The Bone Ranks System
One of the features of Shilla's administrative system that made it distinct among its neighbors was its implementation of a heirarchical organization called "Golpum-jedo" [골품제도], or "Bone Ranks." The "Bone Ranks" derived from the tribal traditions of early Shilla culture and formed the basis of social divisions; an individual's "bone rank" determined what possible governmental office one would hold or even what material possessions and luxuries one may be entitled to own.
The highest two ranks of the Golpum system were the Seonggol 성골 ("sacred bone") and Jingol 진골 ("true bone"). The name of the "sacred bone" ranks suggest that the early leadership of Shilla also held some form of spiritual authority. Those that held the "true bone" rank typically held the highest political office and served on the highest royal councils. Beneath the top ranks were the Dupum 두품 ("head ranks") in which there were six ranks. The highest of these ranks were second only to the "true bone" rank in the general aristocracy and often served as scholars or middle-rank royal officials. The status of women during the Shilla period is not entirely known, but the tradition of determining status upon maternal lines along with paternal lines and the fact that some queens held considerable political power or reigned in their own right (as was the case with Queen Seondeok) suggest that women of this period enjoyed significant freedoms in comparison to later periods of Korean history.
Although the Shilla monarchy attempted to centralize its authority, the upper tiers of the aristocratic class dominated court politics. While the first hundred years of the so-called "Unified Shilla" period was marked by a period of stronger royal authority, the aristocracy continued to monopolize power. The political situation with the monarchy virtually sharing power with a politically strong aristocratic class came characterize much of Korean politics throughout pre-industrial history.
While the king (or queen in some cases) theoretically held absolute power in Shilla, royal aristocratic councils held significant political power. Since the Three Kingdoms period, the "Hwabaek" 화백 served as the chief royal council of Shilla with the purpose of deliberating on the most important administrative decisions of the state such as succession or declarations of war. This council was headed by only an individual of the highest "bone rank." It was the Hwabaek that made the criticial decision of the Shilla court to formally adopt Buddhism as the state religion.