Gusuku period

The Gusuku period (グスク時代) is an era of the history of the Ryukyu Islands corresponding to the spread of sedentary agriculture from Japan and increased social organization, eventually leading to the construction of the namesake gusuku fortresses. Directly following the Shellmidden period, the Gusuku is generally described as beginning in the 11th century, following a dramatic social and economic shift over the previous centuries. The Shellmidden-Gusuku transition has been linked alternatively to migrants from Kyushu, possibly Hayato refugees, or to Yamato influence from the Dazaifu trade outpost on Kikai. Such developments may have also led to the emergence of the Proto-Ryukyuan language.

The period saw extensive agriculture in the archipelago, including the cultivation of foxtail millet, rice, barley, and wheat. Trade occurred with China and Japan, both with the imports of foreign ceramics and the export of the local Kamuiyaki ware. A unique vernacular architecture emerged in the region, featuring elevated village houses. Initially defended by palisades, the rise of the local aji nobility steadily led to the expansion of fortifications, eventually leading to the construction of the namesake gusuku, massive limestone fortresses which proliferated across Okinawa and Amami. Increasing consolidations of aji holdings led to the tripartite division of Okinawa into the Sanzan lordships. The Gusuku period is usually considered to have ended during the first Shō dynasty's hegemony over the island in the early 15th century and the creation of the Ryukyu Kingdom.

Background
The Ryukyu Islands are an island chain on the eastern rim of the East China Sea, adjacent to Taiwan in the southwest and Kyushu to the northeast. Intermittent human settlement of what would become the Ryukyus began in the Late Pleistocene, c. 32,000 years ago. Hunter-gatherer groups originating from neighboring Kyushu began to populate the central and northern Ryukyus c. 5000 BCE, although recent sites suggest possible initial dates of c. 7000 or c. 12,000 BCE. This repopulation of the Ryukyus began the Shellmound or Shellmidden period.

Complex hunter-gatherer societies emerged during the mid-Shellmidden, but polities such as chiefdoms did not emerge, attributed to low populations and carrying capacity prior to the introduction of intensive agriculture. The Shellmidden people exploited plentiful shellfish and reef fish populations. They also hunted the Ryukyu wild boar, the largest mammals on the islands, and possibly tended to domestic pigs.

Although other East Asian populations adopted agriculture long before the beginning of the Common Era, cereal cultivation did not occur in the Ryukyus prior to c. 800 CE, with plant foods largely limited to nuts. Cultivation of taro or other root crops has been theorized, although without conclusive archaeological evidence. The lone unambiguous cultigens from the Shellmidden are bottle gourd seeds recovered from the Okinawan Ireibaru site.

While various other theories positing significant pre-Gusuku cereal agriculture have been proposed, such developments would require the unlikely abandonment of agriculture in lieu of foraging. Agriculture is first archaeologically attested in the Late Shellmidden, evidenced by flotation samples dating to the 800s. However, cultivation remained relatively limited until a rapid expansion in the tenth to twelfth centuries, corresponding to a steady increase of migrants from Japan.

Chronology
Older sources use a much broader definition of the Gusuku period, with the timeframe stretching well into the early Ryukyu Kingdom. Contemporary sources have largely restricted the period as lasting from the 11th century to c. 1429, corresponding to a large societal and economic shift in the central Ryukyu Islands prior to the centralization of the Kingdom of Chūzan and the unification of the Ryukyu Kingdom. Within the Yaeyama Islands (or Sakishima more generally), the period corresponding to the Gusuku is sometimes described as part of the Suku period, divided between the Shinzato Mura (12th–13th centuries) and the Nakamori Period (13th–17th centuries). Due to their close proximity and trade links to Kyushu, the Ōsumi Islands largely follow corresponding archaeological periods in Japan, adopting rice and millet cultivation during the Middle Yayoi period.

Agriculture
Large scale cultivation as the primary means of subsistence in the Central Ryukyus began as the Shellmidden transitioned into the Gusuku. Agriculture likely took root in the Amami Islands in the 8th century, before spreading to the Okinawa Islands 100–200 years later. Rice and millet agriculture spread to Sakishima by the 12th century.

Cereal crops such as rice, barley, wheat, and foxtail millet have been found in Gusuku sites, alongside possibly beans. Southern Okinawa sites mainly grew millet and barley, while rice predominated in northern Okinawa and Amami Ōshima. This rice was initially japonica rice, but tropical O. sativa was likely introduced later via trade with China and Southeast Asia. Farms were initially in low-lying alluvial regions, but gradually shifted to higher slopes. Wheat and barley were largely grown through dryfield cultivation, with irrigation largely limited to rice paddies. Cattle were used to cultivate both varieties of field.

Archaeological examinations of sites at Miyako-jima have revealed similar crops to Okinawa and Amami. Foxtail millet composes the vast majority of finds, alongside smaller numbers of Adzuki beans and broomcorn millet.

Trade and foreign relations
Although trade links (mainly of shells) between Kyushu and the central Ryukyus date to the Yayoi, the transition into Gusuku period saw the import of Chinese ceramics and Japanese soapstone cauldrons alongside native earthenware. The Gusuku people also imported iron knives and magatama from Japan. By the late 12th century, they began importing ceramics (such as Qingbai ware and celadon) directly from China, including types not found in the main Japanese islands. By the 13th century, imports shifted to Longquan celadon, with smaller amounts of Korea, Thai, and Vietnamese ceramics. Traders from the Song Empire were active in the Ryukyu Islands during the Gusuku period, as were Japanese traders from Hakata, Kyushu, and the Dazaifu trade outpost at Kikaijima. Potters on the island of Tokunoshima began to produce the Kamuiyaki ware (or "grey stoneware") in the 11th century. Sulfur mined at Iōjima was likely exported to China via Japan.

During the late 14th century, tribute missions were sent by Okinawan lords to the Ming dynasty and Joseon kingdom. Diplomatic relationships with the Ashikaga shogunate may have been opened by the lord of Shuri in 1403. The Hyōtō Ryūkyū-koku ki, written during the mid-13th century, depicts a group of Japanese travellers shipwrecked on Okinawa and finding themselves in the midst of fierce warfare.

Language
It is unknown what languages were spoken in the Ryukyus during the period. Several theories have been proposed to explain the origins of the Japonic Ryukyuan languages. One theory posits that the Hayato people, possibly speaking a divergent Japonic language, settled in the Ryukyus after the conquest of southern Kyushu by the Yamato state. Other theories describe Proto-Ryukyuan as steadily emerging between the 800s to 1300s from waves of migrants from Kyushu, or as a trade language emerging from Dazaifu traders at Kikaijima.

Architecture
Shellmidden-era construction was largely limited to pit-houses. The agrarian settlements of the Gusuku saw a flourishing of vernacular architecture. Settlements during the 11th to 13th centuries typically comprised several elevated main houses raised on posts, with diameters of 50 cm or more. Pillars within the house were typically spaced by a ken of roughly 100 cm, significantly smaller than the ken spacings of traditional Japanese architecture. Hearths were constructed in the houses, with the largest having two. Elevated storehouses (termed takakura) were positioned 10-15 m from the main structures, generally to the southwest so as to maximize sunlight. Some of these village sites include the remains of metalworking facilities, including pits for the storage of ironsand and hearths equipped with clay tuyeres.

Gusuku
Villages were increasingly placed in defensive positions during the 13th century and surrounded with palisades. By the later portion of the century, some settlements were partially encircled by stone walls. These early fortifications enclosed residential areas of both commoners and elites, as well as some utaki shrines, with satellite villages outside the walls. During the 14th and 15th centuries, these fortifications evolved into the gusuku, massive stone fortresses enclosing elite residences, shrines, and work areas oriented around a central plaza. Gusuku were generally built from coral limestone, although earthen construction is attested in southern Okinawa.

In the north of the island, where coral limestone was not available, ditches dug across ridges were used as fortifications. Gusuku on Amami Ōshima were built for mountain defense, and feature smaller enclosures and large ditches. They were built on "virtually every ridge and headland", protecting rivers and bays, often built in direct line-of-sight of one another. Smaller enclosed fortifications were constructed in Sakishima.

Gusuku vary in size. Smaller structures measuring less than 2000 m2 feature a single enclosure, while much larger gusuku ranging from 10,000-20,000 m2 have multiple. Even larger castles exceeding 40,000 m2 emerged after the end of the Gusuku period.

Society and governance
A class of local nobility, the aji, began to emerge during the early Gusuku period. Local aji initially constructed small gusuku as a show of political power. As particular aji consolidated holdings and absorbed the territories of neighboring lords, the fortifications steadily grew in size and complexity. The most powerful nobles were referred to as aji-osoi ("leader of lords"). They commanded local armies, and held control over less powerful aji within their territories. Larger polities shared power between the ruler and various councilors.

A severe lack of written documentation prior to the 17th century limits the understanding of state and religion during the period. Later myth incorporates various legendary Japanese and Chinese figures into Ryukyuan history. The earliest named ruler, the 11th century Shunten, may have been based after the legendary Emperor Shun.

Emergence of the Ryukyu Kingdom
By the mid-14th century, the various feuding polities of the Okinawa Islands coalesced into three lordships. Collectively referred to as the Sanzan ("three mountains"), they mutually competed for hegemony over the islands. Hokuzan ruled northern Okinawa from Nakijin, Chūzan ruled the central region from Urasoe, and Nanzan ruled the south from Shimajiri-Ōzato.

In 1407, Sho Shishō, previously the aji of Sashiki, seized control of the kingdom of Chūzan and moved the capital of the realm to Shuri. He conquered Hokuzan in 1416. His son Shō Hashi defeated Nanzan in 1429, unifying the three realms under the First Shō dynasty in a common symbolic end date to the Gusuku period. He was recognized by the Yongle Emperor as the "Lord of Ryukyu" in 1422. A 1470 coup d'état by Sho En founded the Second Shō dynasty. The reign of Shō Shin (1477–1526) saw the centralization of the Ryukyu Kingdom at Shuri gusuku and the final subjugation of outlying islands such as the Yaeyama. Local aji were forced to live at Shuri, with agents titled aji-uttchi assigned to administrate their holdings in their place, destroying the last elements of Gusuku period local governance.