Main primary sources for this period include Samguk sagi and Samguk yusa in Korea, and the "Eastern Barbarians" section (東夷傳) from the Book of Wei (魏書) of the Records of the Three Kingdoms in China. Nomenclature Beginning in the 7th century, the name "Samhan" became synonymous with the Three Kingdoms of Korea. The "Han" in the names of the Korean Empire, Daehan Jeguk, and the Republic of Korea (South Korea), Daehan Minguk or Hanguk, are named in reference to the Three Kingdoms of Korea, not the ancient confederacies in the southern Korean Peninsula. According to the Samguk sagi and Samguk yusa, Silla implemented a national policy, "Samhan Unification" (), to integrate Baekje and Goguryeo refugees. In 1982, a memorial stone dating back to 686 was discovered in Cheongju with an inscription: "The Three Han were unified and the domain was expanded." During the Later Silla period, the concepts of Samhan as the ancient confederacies and the Three Kingdoms of Korea were merged. In a letter to an imperial tutor of the Tang dynasty, Choe Chiwon equated Byeonhan to Baekje, Jinhan to Silla, and Mahan to Goguryeo. By the Goryeo period, Samhan became a common name to refer to all of Korea. In his Ten Mandates to his descendants, Wang Geon declared that he had unified the Three Han (Samhan), referring to the Three Kingdoms of Korea. Samhan continued to be a common name for Korea during the Joseon period and was widely referenced in the Annals of the Joseon Dynasty. In China, the Three Kingdoms of Korea were collectively called Samhan since the beginning of the 7th century. The use of the name Samhan to indicate the Three Kingdoms of Korea was widespread in the Tang dynasty. Goguryeo was alternately called Mahan by the Tang dynasty, as evidenced by a Tang document that called Goguryeo generals "Mahan leaders" () in 645. In 651, Emperor Gaozong of Tang sent a message to the king of Baekje referring to the Three Kingdoms of Korea as Samhan. Epitaphs of the Tang dynasty, including those belonging to Baekje, Goguryeo, and Silla refugees and migrants, called the Three Kingdoms of Korea "Samhan", especially Goguryeo. For example, the epitaph of Go Hyeon (), a Tang dynasty general of Goguryeo origin who died in 690, calls him a "Liaodong Samhan man" (). The History of Liao equates Byeonhan to Silla, Jinhan to Buyeo, and Mahan to Goguryeo.