※The underground ruins are not open to the public

A cannon boring machine, known as sankaidai, was a piece of industrial equipment used to drill the inner bore of a cannon barrel.

When casting iron cannons, forming the bore often caused air bubbles to form inside the metal. These imperfections made the cannon dangerous, as the barrel could rupture when fired.

For this reason, the bore was carved after casting, using a machine designed specifically for this purpose, the cannon boring machine.

Alongside the construction of the reverberatory furnace, Shimazu Nariakira began preparing this equipment in 1853. Using the same Dutch technical manual by the military engineer Huguenin, the machine is believed to have been completed after about two years of work.

No physical remains of the facility have been confirmed today. However, a detailed illustration titled “Survey Map of Satsuma,” drawn by Senju Dainosuke of the Saga Domain and now held in Takeo, depicts a cannon-boring facility.

Based on this illustration, the site is thought to have stood near the present-day parking area beside Tsurugane Shrine. A water channel connected to the Yoshino Aqueduct ran behind the facility, and waterwheels powered the machinery, enabling mechanical drilling.

It is said that the facility could bore the barrels of six cannons at once, achieving a level of precision that was remarkably advanced for its time.