The Gusuku Sites and Related Properties of the Kingdom of Ryukyu is an UNESCO World Heritage Site which consists of nine sites all located in Okinawa Prefecture, Japan. The heritage sites include two groves or utaki, the mausoleum Tamaudun, one garden, and five gusuku castles sites, most of which are ruins. The sites were inscribed on the criteria that they were a fine representation of the Ryky Kingdom's culture, whose unique blend of Japanese and Chinese influence made it a crucial economic and cultural junction between several neighboring states.
The Gusuku started to be constructed throughout the islands at the end of the shell-mound period and heralded the Gusuku period and the rise of Aji Chieftains at the approach of the 12th century. During this period, people who had been living in coastlines along low-lying areas had moved to higher ground to build villages inland. Agriculture--such as paddy rice, wheat and millet--was developed further during this period. Groves called utaki were constructed within these villages to serve as sacred grounds for praying to guardian spirits of cultivation. Overseas trading was also opened when the Ryukyu Islands began to create a common culture. The existence of Sueki ware and Chinese ceramics excavated in the Amami Islands region is considered as strong evidence of its cultural development. At the beginning of the 13th century, a steady rise in the interests of the villages saw the emergence of chieftains who were called Aji or Anji and who occupied political positions within these villages. The aji mainly oversaw taxes and conducted religious rites. Trade became more developed and allowed the ajis to increase possession of good harbors in Urasoe, Yomitan, Nakagusuku, Katsuren, Sashiki and Nakijin.