1. Ichirizuka: Small Earth Mounds with Trees Placed Every 4 km
Travelers walking the roads of the Edo period would find earth mounds with trees growing on them on both sides of the path. These structures are known as ichirizuka. According to an explanation from Itabashi Ward, these were built in 1604 (Keicho 9) by order of Tokugawa Ieyasu, placed every one ri (about 4 km or 2.5 miles) along roads starting from Nihonbashi in Edo [5]. The Aomori Prefectural Board of Education also states that they were established nationwide on major roads in the same year by Ieyasu’s command [5]. An explanatory sheet from Edogawa Ward describes them as mounds marking distance for travelers, initiated by orders from the shogunate [5].
Distance markers could have been made of stone pillars. So why were they earth mounds with trees?
2. Why Trees Were Planted on the Earth Mounds
An explanatory board at the Kamikubo ichirizuka in Nagano Prefecture states that distances on old Japanese roads were indicated by large earth mounds, not stone milestones [5]. It is said that the single pine or hackberry tree planted on top of the mound served two purposes: it provided shade for tired travelers, and it helped prevent the earth mound from collapsing and disappearing.
The Aomori Prefectural Board of Education also notes that the trees served as conspicuous markers visible from a distance. They provided a place to rest, offering coolness in summer and shelter from snow in winter [5].
3. How Travelers Used the Mounds to Rest and Make Payments
A guide board at the Koshu Kaido ichirizuka in Suginami Ward states that travelers of that era looked at these mounds to know the distance and to make payments for "dachin" [5]. Dachin refers to the fare paid when having a horse or person carry luggage or one’s body.
The ichirizuka also served as rest stops. As noted in the Aomori Prefecture explanation, they were places to cool off in the shade of the trees in summer and to avoid snow in winter [5].
The type of tree planted was not always hackberry. In Kamikubo, it is said to have been pine or hackberry [5], while the Nomura ichirizuka in Mie Prefecture still has an old hackberry tree said to be 400 years old [5]. It is possible that markers continued with trees chosen according to each region.
4. How Meiji Laws Led to the Removal of the Mounds
In 1876 (Meiji 9), a law titled "Abolition and Destruction of Ichirizuka" was issued, and dismantling progressed nationwide, according to the Itabashi Ward explanation [5]. The Edogawa Ward sheet also states that after the Meiji era, most were dismantled due to the sale of land to private individuals and road expansions [5].
The reason why a law for abolition was issued is not written in the materials reviewed here. One might imagine their role faded due to changes in the times, but this remains speculation.
5. The Shimura Ichirizuka in Itabashi: A Mound That Was Preserved
The Shimura Ichirizuka in Itabashi Ward is the third ichirizuka counted from Edo on the Nakasendo road [5]. It remained even after dismantling progressed in the Meiji era and was designated a national historic site in March 1922 (Taisho 11).
Itabashi Ward writes that when the Nakasendo was widened in 1933 (Showa 8), the mounds were not moved or shaved down [5]. In materials updated in 2020, it is written that members of the local neighborhood association perform maintenance and cleaning every month.
Another Itabashi Ward document states that it is very rare nationwide for an ichirizuka to remain as a pair of two mounds on opposite sides of the road [5]. Shimura is one such example.
Becoming a national historic site likely played a big role in its survival. However, how decisions were made between the designation and the widening construction is not clear from the materials reviewed here.
6. Counting the Surviving Mounds in Kamikubo and Nomura
The Kamikubo ichirizuka in Nagano Prefecture is the 78th from Edo, located about 306 km (about 190 miles) from Edo [5]. Dividing 306 km by 78 gives about 3.9 km, which matches the explanation that the interval between ichirizuka is about 4 km. There were four mounds in Nagiso Town, but this is said to be the only one that retains its original shape.
The Nomura ichirizuka in Mie Prefecture is one of the ichirizuka on the Tokaido road built by Ieyasu in 1604. It became a nationally designated historic site in 1934 (Showa 9), and an old hackberry tree said to be 400 years old remains. It is introduced as the only surviving Tokaido ichirizuka among 12 locations in the prefecture [5].
The types of trees and the ways they survive today differ from place to place.
7. How to Investigate Ichirizuka Near You
If you want to explore this topic, you can look at maps of your local area to see if there are places labeled "Ichirizuka ato" (site of an ichirizuka) or "Ichirizuka." Local libraries with regional materials also offer clues.
If you can visit a place where an ichirizuka remains, try observing the type of tree, the size of the mound, and whether there are two mounds on opposite sides of the road. Comparing the number from Edo written on guide boards with a map can also be enjoyable.
Official information, such as explanations from Itabashi Ward, Aomori Prefecture, and Nagiso Town, is available on their websites and served as the sources for this article.