Katorinoumi (Ancient inland sea of Katori)
The most progressive global warming has begun in the early Jomon period about 6500～5000 years ago. There used to be a vast extent of interior sea called Katorinoumi which included Kasumigaura (Nishiura・Kitaura), Imbanuma and Teganuma.
[Nishiura, Katorinoumi vestiges, is the largest lake among Kasumigaura]
[Nowdays,vast paddy fields spread to the place where there used to be a sea]
The entrance to the sea was opened to the Kashimanada (Pacific ocean) at first, and it was called Kokinuwan (Old Kinu bay) at that time.
After that, the inland sea was getting smaller and smaller by the deposition of sediments which escalated the regression or erosion of Kinu River. In Nara period, it is said that the west-end of the Katorinoumi was around Kawachimachi or Enokiuratsu (Inashiki city shibasaki) and Kinu River flew into the Katorinoumi around there.
[Also Wani River ,where Kashima Jingu’s first tori is enshrined, is part of the Katorinoumi]
In geographical location, Katorinoumi was located in the middle of triangular shaped location of Togoku sansha. (the three major shrines in the eastern provinces)
[Ikisu shrine’s goshuin(left)and Kashima jingu’s goshuin(right)]
Their cultural and economic zones were formed around Katorinoumi. Because Katorinoumi has played a key role in an important logistics hub of water transportation which leads not only to the Tohoku region but also south and north Kanto region, furthermore far west part of Japan. Therefore, there were many competitions with each other with the aim of overwhelming its logistics hub.
[The most part of Katorinoumi has been reclaimed but some parts still remain as a waterway]