Mirrors, which were brought into Japan from the Korean Peninsula and China during the Yayoi period (ca. 400 B.C.-ca. A.D. 250), served as important ceremonial implements for rituals from the Yayoi through the Kofun (ca. 250-ca. 600) periods. The faces of the mirrors were generally convexly curved and polished with mercury, while the backs were decorated with various designs with a knob attached in the center to pass a string through.