Triangular-rimmed mirrors inscribed 景初三年 or 正始元年 (Chinese names of an era, 239 or 240), which apparently commemorated Himiko's dispatching of envoys, were distributed centering upon Kinai region, and also many tumuli from which these mirrors were excavated presumed to have been constructed in the 3rd century - according to the findings of dendrochronology - which match with the dates of Yamatai.
卑弥呼の遣使にちなんだと見られる景初三年、正始元年銘の三角縁神獣鏡が畿内を中心に分布、かつこれらが発掘される古墳の多くは年輪年代学等の結果により3世紀に築造されたと見られ、時代が合致すること。