It is possible that Yamato obtained information on the Tohoku region including the Tsugaru Straits during the Kofun period (tumulus period), when a number of keyhole-shaped mounds including Tsunozuka-kofun (the Tsunozuka Tumulus) in Iwate Prefecture were built in the Tohoku region.
岩手県の角塚古墳をはじめ、東北地方に多数の前方後円墳が築造された古墳時代には、津軽海峡の存在をはじめとする東北地方についての情報を大和が得ていた可能性もある。