Hara Castle was the local feudal lord Arima’s important castle in the Age of Civil Wars. In 1637 (Kanei 14), it became the main battlefield of an uprising known as the Shimabara Rebellion.
Hara Castle was built on a cliff jutting into the sea. Its surroundings comprise about 4 kilometers, including the main, second and third enclosures; Amakusa enclosure and Hatoyama Promontory. In the east was the Ariake Sea, while the west and north were surrounded by swamps except for a small part, where the land made a natural fortress.
The main enclosure was surrounded by stone walls and the main gate was built in a square shape, which were the characteristics of modern castles: masonry structure technique accomplished in the Nobunaga Oda and Hideyoshi Toyotomi periods such as high stone walls, roof tiles and structures built on foundation stones. On the other hand, the second and third enclosures were built on the ground, based on the natural landscape.
The construction of Hara Castle started in 1599 (Keicho 4) and completed in 1604 (Keicho 9). The report from Jesuits stated that a new castle was under construction which was much better-located and much-stronger built than Hinoe Castle ? the local feudal lord Harunobu Arima had lived after the Battle of Bunroku and Keicho. The report also stated that there were Harunobu’s mansion, retainers’ mansions and a three-storied watchtower with an ammunition chamber and provision storage inside Hara Castle. After the transfer of Naozumi (Harunobu Arima’s son) to Usuki-gun in Hyuganokuni(modern-day Nobeoka City in Miyazaki Prefecture), the castle fell to ruins due to the 1-Castle-in-1-Domain Regulation taking effect the following year.
Archaeological excavations have been carried out since 1992 (Heisei 4). Many relics have been unearthed from the main enclosure. Particularly, Christian artifacts associated with the Shimabara Rebellion have been excavated including crosses, medals and rosary beads. The ruins of the main gate, the stone wall bases of the watchtower, and the gateway corresponding to the main entrance of the castle ? which were all demolished and buried by shogunate soldiers after the rebellion ? have also been found. They indicate how the shogunate dealt with the uprisings in Shimabara and Amakusa.
On May 30th, 1938 (Showa 13), Hara Castle Ruins were designated as a National Historic Relic Site.