In regions north of Mutsu, roads with the Tokaido name are found here and there. If they are legacies of ancient times, it is likely that the Tokaido existed as a branch line in regions farther north.
それより北にも各地に東海道と呼ばれる道が断片的に存在し、それが古代の名残りだとすると、さらに北でも支線として存在した可能性が高い。