Furthermore, it can be seen from the "Arima Kachu Nobeoka Joka Yashiki tsuki Ezu" (Arima Family Nobeoka-jo Castle Residential Drawing) (held by Meiji University) that the area in between Inoue-jo Castle and Furushiro and to the east of Inoue-jo Castle, is spotted with swamps thought to be ponds left over from the changing course of the rivers.
さらに、井上城と古城の間や井上城の東には、河跡湖と思われる沼池の点在していたことが『有馬家中延岡城下屋敷付絵図』（明治大学所蔵）からも読みとれる。