Mie Castle was built on the northern mouth of Naha Port in 1546 by King Shō Sei. It was built to defend the Port and city of Naha, alongside its sister Yarazamori Castle. Between the two castles, an iron chain boom-net could be drawn up to deny ships access to the harbor. Mie Castle, although the smaller of the two, was armed with 7–9 cm cannons. The defenders were also armed with pikes and native-made hand cannons. These defenses were intended for use against pirates, however they proved successful in driving away the fleet of Satsuma during their 1609 invasion. The castle would continue to be used for anti-piracy, however it became generally used by civilians for seeing ships' departures.