 South Korean claims are partly based on references to an island called "Usan-do" () in various medieval historical records, maps, and encyclopedia such as "Samguk Sagi", "Annals of Joseon Dynasty", "Dongguk Yeoji Seungnam", and "Dongguk munhon bigo".According to the South Korean view, these refer to today's Liancourt Rocks.Japanese researchers of these documents have claimed the various references to Usan-do refer at different times to Jukdo, its neighboring island Ulleungdo, or a non-existent island between Ulleungdo and Korea.