The establishment of Cheonghaejin by Jang Bogo in 828 during the reign of King Heungdeok was a monumental event that reshaped the maritime order of East Asia and ushered in a golden age of sea trade in the late Unified Silla period. At the time, Unified Silla was experiencing significant instability due to the weakening central government and the rise of local powers. More critically, the southwestern coast was plagued by rampant piracy. These pirates not only plundered merchant ships traveling between Silla, Tang China, and Japan but also committed atrocities by abducting Silla people and selling them as slaves in Tang China. This severely disrupted maritime trade and posed a grave threat to national security. Against this backdrop, Jang Bogo, who had served as a military officer in Tang China and gained a profound understanding of international affairs and the importance of maritime trade, returned to his homeland. Deeply concerned by the severity of the pirate problem, he approached King Heungdeok in 828 (the 3rd year of King Heungdeok's reign). Jang Bogo proposed establishing a naval base at Cheonghae (Wando) to suppress pirates and stabilize maritime trade. Recognizing Jang Bogo's exceptional insight and capabilities, King Heungdeok accepted his proposal and ordered the establishment of Cheonghaejin on Wando Island. Jang Bogo then proceeded to construct a formidable maritime base equipped with strong fortifications and shipbuilding facilities, and he trained a powerful navy to eradicate the pirates. Following the establishment of Cheonghaejin, Jang Bogo's achievements were remarkable. Within just a few years, he completely suppressed the pirates along the southwestern coast, ensuring maritime safety. Building on this success, Cheonghaejin rapidly emerged as the central hub of East Asian maritime trade, connecting Silla, Tang China, and Japan. Jang Bogo established his own extensive trade network, accumulating immense wealth, and Cheonghaejin functioned as a bustling international port and a center for cultural exchange. He earned the title "Maritime King" for his unparalleled dominance of the seas. Although his growing power eventually led to friction with the Silla central government, culminating in his tragic assassination by Yeom Jang in 846, Jang Bogo's establishment of Cheonghaejin was a decisive contribution to reshaping the East Asian maritime order and elevating Silla's international standing. It remains a historical event that inspired future dreams of a powerful maritime nation.