Korea has a long history of naval activity. In the late 4th century during the Three Kingdoms Period, Goguryeo defeated Baekje, fielding amphibious forces of 40,000 men in the process. In 732, the Balhae navy "attacked the Shandong peninsula and destroyed the biggest seaport of the Tang Empire in the east – Dengzhou." In the 9th century, Commissioner Chang Bogo of Unified Silla established a maritime base called Cheonghaejin on an island to foster trading with China and Japan, and to eradicate pirates.