Indeed, Edo was established west of the Sumidagawa River estuary which served as a provincial border between Musashi Province and Shimosa Province, and Hibiya inlet stretched across the area where the Edo Castle was later constructed.
当時の江戸は、武蔵国と下総国の国境である隅田川の河口の西に位置し、日比谷入江と呼ばれる入江が、後の江戸城の間近に入り込んでいた。