Military garrisons in Silla originally were established at strategic locations to defend the country's land frontiers, the Northern Garrison (Pukchin) at Samch'ok and the P'aegang-jin at modern P'yongsan being prime examples. But as the threat of piracy to Silla's maritime commerce intensified, a succession of garrisons also came to be established at important coastal points, such as the Ch'onghae Garrison (on Wando island), Tangsong Garrison (at modern Namyang not far southwest of Seoul), and Hyolgu Garrison (on Kanghwa Island). The most important of these was the Ch'onghae Garrison.

The Ch'onghae Garrison was established in 828 by Chang Po-go. He had journeyed to China as a young man and had pursued a successful military career in the service of T'ang. Outraged at the frequent incidents of his countrymen being captured by sea marauders and sold into slavery, Chang Po-go returned to Silla and appealed to King Hungdok (826-836) to formally establish a garrison on Wando, athwart the vital sea lanes in Korea's southern waters, where he already had created a strong military base.

The king consented and appointed Chang to command the Ch'onghae Garrison. With a force of 10,000 men, very much in the nature of his own private army, he patrolled Silla's coastal waters and put an end to the depredations of Chinese pirates. At the same time, he controlled a flourishing trade with China and Japan and became, in effect, the master of the Yellow Sea. Chang Po-go not only ruled the sea-lanes, but he intruded himself as well into the thick of the political strife in the capital. The military support he provided enabled Kim U-jing (King Sinmu), who came to him for help after losing out in an earlier struggle for the throne, to storm the capital and claim the kingship (839). A few years later, however, the protests of the capital aristocracy prevented King Muns6ng (839-857; Sinmu's son) from taking Chang Po-go's daughter as his second queen, and in the end this episode led to Chang's death at the hands of an assassin (846). Not long thereafter the Ch'onghae Garrison itself was abolished (851).

For a time Chang Po-go and his Ch'onghae Garrison command had represented a powerful force indeed. But he failed in his efforts to participate directly in the politics of the capital, nor was he able to create an independent political force that might contend for supremacy with the government in Kyongju. The capital aristocracy was torn by schism and its power had begun to crumble, but it still was strong enough to preserve the bone rank system on which its dominance rested.

Thus the islander Chang Pogo, guilty of heresy against the Silla social order, met his downfall, and the 10,000 troops under his command were removed to Pyokkol county (modern Kimje) where they no longer could pose the threat of insurrection. But other military garrisons had developed in much the same way as had that at Ch'onghae, and before long these would serve as sources of military support for the ambitions of powerful gentry families in the Silla countryside.

Military Organizations of Ancient Korea

Introduction
Re-organization of the Military System
Emergence of Powerful Military Garrisons