Fortified castles on the island of Okinawa, southwestern Japan, date from approximately AD 1200 to 1600. These castles are termed gusuku in Okinawan dialect. The larger of these multifunctional sites usually contained a number of different activity areas (Pearson 1992; 1997; 1999). Katsuren Castle, located on the east coast of Okinawa, is one example (FIGURE 1). Extensive excavation and restoration of the castle (Asato 1990) suggest that it was approximately 12,000 sq. m in size, and included four enclosures. The smallest, highest and most protected enclosure was the sacred precinct. The second enclosure contained the residential palace, and the third was an area in front of the residential palace used for assemblies. The fourth, lowest enclosure included storage, a work place for artisans and a well. The largest castles ranged from 38,000 to 43,000 sq. m (Pearson 1962: 268).
[Figure 1 ILLUSTRATION OMITTED]
Okinawan histories, such as the Chuzan Seikan (Haneiji 1983) written in the 17th century, describe competition for power throughout the island in the form of various confederacies until the emergence of three polities in the 14th century. These polities were located in the north, central region and south of the island, and they were unified by the central polity, the Chuzan Kingdom, in AD 1429. Okinawan prefectural archaeologists have located 192 gusuku sites (Okinawa Ken 1983), shown as circles, squares and triangles in FIGURE 2. All of these castles were built within the period c. AD 1200-1554. By 1429 Shuri Castle was the centre of the Chuzan Kingdom, and by 1554 only four specialized castles throughout the island were maintained (Pearson 1997: 126). In 1609 the Chuzan Kingdom was invaded by the Satsuma fiefdom of southern Japan, which controlled it until 1879. It became known as the Ryukyu Kingdom.
[Figure 2 ILLUSTRATION OMITTED]
Asato (1990: 128-37; 1998) published a discussion of site groupings and their distribution, and their development into 17th- and 18th-century political divisions (magiri) and cultural subgroups. Based on a non-statistical analysis, he traced the development of prehistoric shell-mound site groups, to subgroups sharing certain kinds of pottery temper, to castle groups and finally to administrative sub units at the time of the Ryukyu Kingdom (AD 1609-1879). Our study parallels and extends his historical interpretation by using a geographical information system to analyse the distribution of fortified castles in relation to each other and the soils of the island.
Soils and subsistence activities
During the first half of the 2nd millennium, subsistence cultivation on Okinawa was based on a combination of dry-field wheat (Triticum aestivum), barley (Hordeum vulgare), foxtail millet (Setaria italica), broomcorn millet (Panicum miliaceum) and irrigated rice (Oryza sativa) (Sasaki 1973; Asato 1990). A preponderance of wheat, barley, foxtail millet and broomcorn millet in flotation samples analysed by Takamiya (1997) may indicate that dry-field farming was predominant; however, only two sites have been analysed and the samples are relatively small. In addition, taro was grown extensively in areas with adequate moisture (Sasaki 1973). Takamiya (1997) suggests that rice was not a primary crop on the island because it matures during the typhoon season and could therefore be easily ruined.
Chinzei et al. (1967) grouped the soils of Okinawa into five basic types (podzolics, forest, alluvium, regosols and lithosols). We have made a further subdivision within lithosols, and group the Okinawan soils into six types (see FIGURE 2). The reddish podzolics of central and northern Okinawa are derived from metamorphosed sediments of Palaeozoic Age, principally phyllites and feldspathic sandstone. The brown forest soils are found primarily in the central region of the island, and are derived from raised limestone coral. The …