Okayama Plain - Okayama Heiya

A plain in the southern part of Okayama Prefecture facing the Seto Inland Sea. It is an alluvial plain formed by the deposition of the three major rivers, Yoshii River, Asahi River, and Takahashi River, as well as the Sunagawa River, Sasagase River, and Ashimori River. As part of the Seto Inland Sea, which had once been a large bay known as Kibi no Anaumi in ancient times, was filled in, the former islands became scattered hills in the plain, and Kojima became a torii (tied island) and became the Kojima Peninsula in the 16th and early 17th centuries. The area has a long history of development, and Yayoi-style relics and ruins have been excavated underground in the plain in Tsushima, Kita-ku, Okayama City, and Sho, Kurashiki City. The southern limit of the jori ruins is unclear, but they can be clearly seen east of Okayama City from the JR Sanyo Main Line to the Sencho Plain on the east bank of the Yoshii River, and west of that along the old Sanyo Road and National Route 180. The plains are home to many ancient historical sites and ruins, including Ryoguzan Tomb, Tsukuriyama Tomb, Tsukuriyama Tomb, the remains of Bizen Kokufu, Bitchu Kokufu, Kibitsu Shrine, Kibitsuhiko Shrine, and others. In the Middle Ages, Daianji Manor and Shikata Manor were located near Okayama City. Land reclamation began with the reclamation of the areas around Kurashiki and Hayashima by Ukita Hideie in 1584 (Tensho 12), followed by Okishinden and other areas by the Okayama Domain in the 17th century, Kojoshinden in the 19th century, Fujita Gumi after the Meiji period, and the Ministry of Agriculture and Forestry after World War II. Meanwhile, many new fields were developed in southern Kurashiki and Mizushima, and after World War II, waterfront industrial land was created on a large scale in Mizushima. Okayama is the center of economic activity in Okayama Prefecture and a rich grain-producing region, with Okayama City and Kurashiki City serving as commercial centers and industry developing along the coast.

[Shogo Yuihama]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

岡山県南部、瀬戸内海に面する平野。吉井川、旭(あさひ)川、高梁(たかはし)川の三大河川や砂川、笹ヶ瀬(ささがせ)川、足守(あしもり)川などの堆積(たいせき)作用により形成された沖積平野である。古い時代に吉備(きび)の穴海として広く湾入していた瀬戸内海の一部を埋めたため、かつての島は平野のなかに散在する丘陵になっており、児島(こじま)も16世紀から17世紀初頭には陸繋島(りくけいとう)となって児島半島となった。開発の歴史は古く、岡山市北区津島や倉敷市庄(しょう)などでは平野の地下から弥生(やよい)式の遺物、遺跡が発掘された。条里遺構の南限は不明瞭(ふめいりょう)であるが、岡山市以東ではJR山陽本線沿線から吉井川東岸の千町(せんちょう)平野にかけて、以西では旧山陽道や国道180号沿線に顕著に認められる。平野には両宮山(りょうぐうざん)古墳、造山(つくりやま)古墳、作山(つくりやま)古墳、備前(びぜん)国府跡、備中(びっちゅう)国府跡、吉備津神社、吉備津彦神社、その他の古代の史跡、遺跡が多い。岡山市付近では中世には大安寺荘、鹿田(しかた)荘などがあった。干拓では1584年（天正12）宇喜多秀家(うきたひでいえ)による倉敷、早島付近の開墾を初めとして、岡山藩による17世紀の沖新田その他、19世紀の興除(こうじょ)新田、明治以後は藤田組、第二次世界大戦後は農林省による干拓が行われた。一方、倉敷南部や水島でも多くの新田が開発され、第二次世界大戦後は水島で臨海工業用地が大規模に造成された。岡山県の経済活動の中心で、豊かな穀倉地帯であり、また岡山市、倉敷市が商業の中心をなし、臨海部は工業が発達している。

［由比浜省吾］

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