Sengokuiwa, the Gigantic Rock, in River Daido

At a steep curve of the current of the River Daido, there is a gigantic rock called Sengokuiwa. The current hits this rock so that it prevents levees from breaking, which results in saving the amount of rice worth sengoku [which means approximately 2,500 bales]. That is why this rock is called Sengokuiwa [Sengoku rock].