The Yayoi period is marked by specific centers specializing in magatama and the widespread trade of magatama. The period is marked by the formation of power centers that came to be individual states. The development of weapons increased in this period to protect increasingly developed rice fields and fishing rights. Trade greatly increased in this period, as did the specialization of production of certain items, including magatama. Magatama producing areas exchanged their product with other products, specifically rice, leading to the widespread distribution of magatama across Japan. Magatama were commonly used to create necklaces and bracelets worn on the wrists or ankles. The necklace was typically constructed of jadeite magatama separated by cylindrical bored-holed pieces of jasper. Small beads of dark-blue glass are also not uncommon on the necklace. The bracelet was typically also used shells from the coastal areas of Shikoku and the Inland Sea, wood, and bronze. In this period the use of the mirror, sword, and jewels as status symbols for village, and later regional leaders of all kinds, emerged in the Yayoi period, and point to the origin of the mirror, sword, and magatama as the Imperial Regalia of Japan.