The Imperial Family is identified with three sacred objects — the mirror, sword and curved jewel, or magatama. According to mythology, they were handed by Amaterasu, the sun goddess, to Ninigi when he descended from heaven and then passed along the imperial line. Historically, however, when exactly the three objects became symbols of the emperor’s family is not clear. They were already important religious symbols by the Middle Yayoi Period, and are abundant in the tombs of the Kofun Period. At some point they coalesced to indicate supreme authority. Now the mirror is supposedly in Ise Jingu, the sword at Atsuta Jinja and the magatama in the imperial palace in Tokyo.
The roots of the mirror lie in China. Han Chinese mirrors were common in northwestern Kyushu by Middle Yayoi, though these were preceded by mirrors from Korea a bit earlier. It might have been simply a talisman to ward off evil. Mirrors were a major burial object in Kofun Period tombs, especially the earlier ones, but they were not necessarily associated with the other symbols. It is not known whether the ideas surrounding the mirror were imported from the continent together with the mirror, or whether the Yayoi people simply saw the mirror as a useful symbol for ideas they already had. At any rate in the Yamato age it became associated with the supreme goddess, Amaterasu, ancestor of the emperor.
The sword (or weapon) would seem to be a symbol of male virility with origins in the stone phallic symbols of Jomon times. By late Jomon the symbols looked more like stone swords than phalluses. Bronze swords and spears were imported from Korea from the end of the Early Yayoi period. Later ritual forms of the weapons were manufactured in Japan and are common in Yayoi sites — spears in northwestern Kyushu and swords in western Honshu and Shikoku. Swords are common in Kofun Period burials, especially the later ones. In Europe too they were symbols of spiritual authority (think of Excalibur), and Mircea Eliade has written of the religious significance of metal to early humans as a precious gift from a livinig earth.
The magatama’s origins are more controversial. These curved jewels of jadeite are common in Kofun Period burials, and are common also in Korean sites of the same age. This fact seems to have led archaeologists to conclude that the magatama originated in Korea. but magatama are found in Yayoi sites, too. No one seems to know what the shape represents exactly, but It is said to represent the soul. Tama in Japanese means jewel or ball, but originally also meant soul (as in tamashi, the Japanese word for soul or spirit). Some people say it’s a reduction of yin-yang to a single element, as if to signify the most basic element of life. I asked a leading archaeologist at my university about it, and he told me something rather surprising – he suspects it represents a hook, to ‘hook evil’ as it were. In other words a Yayoi era omamori! Look at the magatama in the bottom row below and you can see what he means…