The Japanese expedition to Taiwan in 1874 -- ostensibly a punitive action against indigenous Paiwan people who had killed shipwrecked Ryukyuan sailors -- exposed the Qing dynasty's vulnerability on its island frontier. Shen Baozhen, dispatched to strengthen Taiwan's defenses, chose a site in Anping District for a Western-style fortification. Construction began in 1874 and finished in 1876, producing the Erkunshen Battery -- a name that never caught on the way Eternal Golden Castle did. The castle was built to European specifications, with a square bastion plan designed to eliminate blind spots and provide overlapping fields of fire. Its moat surrounded the entire structure, and its walls were thick enough to absorb cannon fire from approaching warships.

The castle's first test came in 1884 during the Sino-French War, when French naval forces clashed with Chinese defenders along Taiwan's coast. The Eternal Golden Castle held. Its second came in 1895, when the Qing dynasty ceded Taiwan to Japan under the Treaty of Shimonoseki. Rather than accept Japanese rule, local leaders proclaimed the Republic of Formosa and attempted to resist the invasion. Taiwanese fighters used the Eternal Golden Castle as a defensive position against Japanese battleships -- one of the few moments in history when a short-lived republic attempted to hold a fortress against an imperial navy. The resistance failed. Under Japanese control, the castle lost its military value. During the Russo-Japanese War, the imperial government sold some of the fort's cannons -- the very weapons meant to defend the island -- stripping the fortress of the hardware that gave it purpose.

Today, the Eternal Golden Castle has traded warfare for leisure. A park surrounds the castle grounds where families spread picnic blankets. Rental paddle boats let visitors circle the moat that once kept attackers at bay. Evening brings occasional music performances to the site, and actors sometimes fire the single remaining artillery piece -- the last cannon the Japanese did not sell -- to give visitors a taste of what the fortress was designed to do. The bastion walls still stand, their square geometry with four corner bastions visible from above, a military architecture lesson written in brick and earth. For the price of an NT$70 admission ticket, visitors can walk the ramparts where Formosan republicans once aimed cannons at Japanese warships, stand in gun emplacements that faced the Sino-French conflict, and contemplate the irony of a fortress whose occupiers sold its defenses for scrap.