In this episode: 

-Josh apologizes for getting ahead of himself and slooooooooows his Koshi roll

-More super old references to Koshi Country (future Kokuriku areas) in Japan

-First recorded castle walls in existence were built on the borders of Koshikuni by the Yamata government in response to Ezo threat in the north 

Nuttari Fence (沼垂柵)

https://www.city.niigata.lg.jp/higashi/torikumi/seisaku/nutarinoki/nutari_explanation.html

https://smcb.jp/communities/24955/topics/1737360

Iwafune Fence

(岩船柵) https://main-oosaki.ssl-lolipop.jp/allstar/1856/

https://smcb.jp/communities/24955/topics/1737360

"Nihon Shoki" (日本書紀)

"Shoku Nihongi" (続日本紀)