The ken, a sword with a straight, double-edged blade based on Chinese prototypes, was used in Japan from at least the third century until the sixth century. At the end of this period the double-edged sword was gradually superceded by the single edged type, from which all later Japanese swords developed. This ken was discovered in one of Japan's most famous early burial mounds, known as the Edo Funayama Kofun (burial mound), located in Kumamato Prefecture, on Kyushu Island, in southern Japan. The mound, which was first excavated in 1873, yielded many rare items, including jewelry, crowns, ceremonial shows, armor parts, mirrors and several swords, all of very high quality. Swords of this period are extremely rare and show the earliest stage in the development of Japanese sword blades. This blade was given to the Metropolitan Museum in 1906 as part of an exchange of art objects with the Imperial Museum in Tokyo. In 1965 the remaining finds from the excavation were officially designated as National Treasures, the highest ranking given to cultural objects in Japan. They are now in the collection of the Tokyo National Museum.