Wiryeseong was the name of two early capitals of Baekje, one of the Three Kingdoms of Korea. Both are believed to have been in the modern-day Seoul area. According to Samguk Sagi (the oldest surviving Korean history book, written in the 12th century), Onjo, the son of Goguryeo’s founder Jumong, founded the nation of Sipje (십제, 十濟; later became Baekje) on Wiryeseong in 18 BC, while his elder brother Biryu established himself in Michuhol (미추홀, 彌鄒忽) further to the west. The location of Michuhol is usually believed to be present-day Incheon.