Pophung expanded his domain by conquering Pon Kaya, the largest of the Kaya states, in 532. His successor, Chinhung (r. 540-576), expanded the state further, making Silla a serious contender for control of the entire peninsula. With Silla's ally Paekche, Chinhung launched an inva-sion of the Han River basin during the years from 551 to 554. Under his general K6ch'ilbu, the Silla forces and their Paekche allies were success-ful in driving Kogury6 out of the Han valley. Then turning against his erstwhile partner and severing a 120-year alliance, Chinhung attacked Paekche, whose King Song perished at the battle of Kwansan in 554. The Han River basin was now part of the Silla state. This gave Silla access to the Yellow Sea and brought Silla into direct contact with China. It also ·eparated Paekche from Koguryo, making cooperation between the two. tates more difficult. Perhaps most importantly, the Han River basin withits rich farmlands and its iron deposits enriched the kingdom. Chinhungthen conquered Tae Kaya in 562, ending the independent existence ofthe Kaya states and bringing the entire Naktong valley under Sillan con-trol. This step excluded direct Japanese influence in Korea for over 1,000years. Silla forces then invaded the former territory of the Okch6 alongthe Hamgyong coast, inflicting another defeat on Kogury6. Chinhung cel-brated his military triumphs by erecting what are known as the Four Ste-lae of King Chinhung. These were placed at strategic points in his domain at Chungnyong Pass, at Pukhansan in north Seoul, and in the H wangch' o and Maullyong passes in Hamgyong Province and have survived to the present, providing us with among the earliest Sillan written documents. THE BONE-RANKS, THE HWABAEK, AND THE HWARANG 'ilia gradually evolved from a confederation of chiefdoms into a cen-tralized state. As it did, three prominent social and political institutions d v loped: the bone-rank system, the Hwabaek (Council of Notables), and th l,warang (fl w r boy ). All three reflected two feature of Silla. Fir t, Start reading here.
42 Chapter 2 it appears to have been more elaborately stratified than either Koguryo or Paekche .14 Second, as local chiefs were transformed into an aristocracy they retained considerable power and Silla became a state where power was shared between the monarch and powerful aristocratic families. The most pro minent feature of Silla was the kalp'um (bone-ranks) a sys-tem of hierar chical ranks in Silla corresponding to hereditary bloodlines . It emerged in the sixth century as local chiefs became aristocrats. Each rank conferre d a variety of special privileges such as qualification for of-fice or the right to po ssess certain kinds of material goods.15 The two top bone -ranks were the songgal (sacred bone), which was confined to the main bran ch of the royal Kim descent group, and the chin'gol (true bone), whose mem bers were the cadet branches of the royal family, perhaps members of the Pak and Sok royal consort families, and the royal house of Pon Kaya. These made up the highest level of the aristocracy. Originally the chin 'gal