This foundation stone belonged to Suigetsuzan Entsuji Temple, which was opened in 1353 by Daichi Sokei (1290-1366) after he arrived in Kazusa at the invitation of the Arima clan. The stone is made of natural basalt that has been roughly molded into the shape of an asymmetric pentagon with a raised center in the shape of a circle. The temple had a large main gate and many halls, but it was ultimately abandoned after the Arima clan converted to Christianity during the Tensho era. Today, only this stone and a few other artifacts remain.