In October 1637, the Shimabara-Amakusa Rebellion, led by Amakusa Shiro Tokisada, achieved successes in the initial battles at Shimago and killed Miyake Tobei, the temporary castellan of Tomioka Castle, at Hondo. encourage by the success, they fiercely attacked Tomioka Castle and came close to victory. However, Tomioka Castle did not fall, they abruptly decided to give up and withdrew to Shimabara. It is said that, because it was a good harbor with enough width and depth, this is where the forces embarked to Shimabara after having failed to seize Tomioka Castle. This monument is designed with natural stone as a ship and a cross as a mast.