Ōshū Kaidō
National Route 4 was preceded by the Tōsandō, a road initially established during the Asuka period as a road linking Kinai (now Kyoto and Nara) to what is now the vicinity of Morioka, Iwate. The portion of the Tōsandō that was later incorporated into National Route 4 lies between Tochigi Prefecture and Iwate Prefecture. The next development of the route came along with the creation of the Ōshū Kaidō (奥州街道) and Nikkō Kaidō (日光街道) as two of the five routes of the Edo period. They were established by Tokugawa Ieyasu for government officials traveling through the area to connect Edo (modern-day Tokyo) with Mutsu Province and the present-day city of Shirakawa, Fukushima Prefecture, Japan. There were also many roads that connected to the Ōshū Kaidō that are included in National Route 4. One such sub-route was the Sendaidō (仙台道), which connected Mutsu Province with Sendai. From Sendai, the Matsumaedō (松前道) connected Sendai with Cape Tappi and indirectly to Hakodate on the southern shore of Hokkaido on the Tsugaru Strait. Though the Ōshū Kaidō has only 27 post stations, there were over 100 designated post stations when the subroutes are included. Some sections and markers of the Ōshū Kaidō in their original state can still be found alongside National Route 4, the Hachinohe Expressway, and Tōhoku Expressway.