The ruins of Nakijin Castle are located on the Motobu Peninsula in the northern part of Okinawa, Japan. The castle was built in the 13th century during the Sanzan, or three kingdoms, period. During this time, the island of Okinawa was divided into northern, central, and southern kingdoms, each of which was controlled by a different ruler. Nakijin Castle was the seat of the northern kingdom (known as Hokuzan) until the three kingdoms were unified by Sho Hashi in 1429.