張保皐
In East Asia by the ninth century, populations centered mostly around merchant activities in coastal Shandong and Jiangsu provinces. Wealthy benefactors, including Jang Bogo established Silla Buddhist temples in the region. Jang Bogo had become incensed at the treatment of his fellow countrymen, who in the unstable milieu of late Tang often fell victim to coastal pirates or inland bandits. After returning to Silla around 825, and in possession of a formidable private fleet headquartered at Cheonghae (Wando), Jang Bogo petitioned the Silla king Heungdeok (r. 826–836) to establish a permanent maritime garrison to protect Silla merchant activities in the Yellow Sea. Heungdeok agreed and in 828 formally established the Cheonghae (淸海, "clear sea") Garrison(청해진) at what is today Wando island off Korea's South Jeolla province. Heungdeok gave Jang an army of 10,000 men to establish and man the defensive works. The remnants of Cheonghae Garrison can still be seen on Jang islet just off Wando's southern coast. Jang's force, though nominally bequeathed by the Silla king, was effectively under his own control. Jang became arbiter of Yellow Sea commerce and navigation.