The main city of Ulleung-do is the port of Dodong, from which ferries to and from the Korean mainland depart. Archeological evidence indicates that the island has been inhabited since the 1st millenium BC. The first confirmed historical reference to Ulleung-do is in the Samguk Sagi for the year 512. In that year, the Silla general Lee Sabu conquered the island, which had previously been the autonomous nation of Usan-guk. Some accounts relate that he used a number of wooden lions to intimidate the population, threatening to turn them loose unless they surrendered. Usan-guk did not remain under the Silla yoke, however, and the island did not become a permanent political part of Korea until 930, when it was annexed by Goryeo. Remote as it is from the Korean mainland, Ulleung-do was a recurrent security headache for the Goryeo and Joseon dynasties. It was devastated by Jurchen pirate raids in the 11th century, and by Japanese pirate raids in the 14th century. A clash with Japan over fishing rights in the 1690s was precipitated by the Korean fisherman An Yongbok. In response to these difficulties, Joseon adopted an "empty-island" policy which however proved impossible to enforce. The empty-island policy was officially rescinded in 1881, after which the government sought to encourage additional emigration to Ulleung-do.