Hama Castle was constructed next to the medieval port of Shimabara. The lord of the castle was Shimabara Sumishige, a vassal of the Arima Clan that ruled the area. According to History of Japan by Frois, Sumishige hoped for the propagation of Christianity, and his acceptance of Christianity served as the impetus for the penetration of Christianity in the Shimabara region. Although the landscape of the area around the site of Hama Castle has changed due to the development of the castle town in the Edo Period and the Catastrophe in Shimabara in 1792, this is a significant historical site related to the propagation of Christianity to Shimabara.