Gusuku Sites and the Kingdom of Ryukyu

In the year 2000, the nine cultural properties of Shuri Castle, Tamaudun tombs, Sonohyan Utaki Stone Gate, Shikinaen, Seifa Utaki, Nakagusuku Castle Ruins, Katsuren Castle Ruins, Zakimi Castle Ruins, Nakijin Castle Ruins, were registered as Japan's eleventh world heritage, "Gusuku Sites and Related Properties of the Kingdom of Ryukyu".
"Gusuku" is expressed in the kanji character for castle, and in general interpreted to mean castles. The total number of gusuku in the main island of Okinawa alone exceeds 200, and adding ones in the Amami Islands in Kagoshima Prefecture to Miyako Islands and Yaeyama Islands in Okinawa Prefecture, where gusuku structures differ, would reach 300.
Gusuku is said to have developed since about the thirteenth century as fortress of Aji or local clans. The main feature of Gusuku is stonewalling that seems to intend to make beautiful curve lines, and there are several construction varieties. In the Nozuradumi style, unprocessed stones are piled up. This style is older than other methods. On the other hand, rectangular solid stones are piled up one by one in the Nunodumi style, and in the Aikatadumi style, stones cut in quadrangle, pentagonal, and hexagonal shapes are assembled in a variety of ways.
Another major feature of gusuku is utaki, where gods were believed to descend, and "uganju", where people worshipped gods. some gusuku lack stonewalls and have only utaki, which are still places of worship. In this way, gusuku are not only defense facilities but also a spiritual base of Ryukyuans.