Japanese History Tokyo Rivers

The Tone River

Sometimes called the biggest river in Japan, though it’s actually not, this unruly river unites much of the Kanto area.

The Tonegawa

(useful root river, but actual meaning isn’t known)

The Tone River flowing past Sekiyado Castle in Chiba Prefecture.
Notice Mt. Fuji in the background.

I’ve often heard that the 利根川 Tonegawa Tone River is the longest river in Japan. Actually, it’s not. The 信濃川 Shinanogawa Shinano River[i] is the longest, but the Tonegawa has the largest watershed. That is to say, we’re not referring to a single river, but the entire network of rivers and tributaries that veer off from the source like the veins of a leaf. And like a leaf, there is an ending point for the veins. These are the natural boundaries that stop the river, where the river loses energy and “dies,” or where it empties out into the sea. On a map, you can actually pinpoint these boundaries and chart the watershed, which is the entire water system from start(s) to finish(es).

Example of a watershed. Hopefully the leaf analogy makes sense now.

By strict definition, the river begins on the 大水上山 Ōminakami Yama Ōminakami Mountains (literally, “Great Headwaters Mountains[ii]”) in Gunma Prefecture and empties out into the Pacific Ocean at 銚子 Chōshi in Chiba Prefecture. That said, the entire watershed is littered with towns and waterworks which reference the river, despite being off the official government designated course. The Arakawa and Edogawa are often cited unofficially as exit points of the river. You can clearly see on one of the maps on my Sumidagawa article that in the earliest days of the Edo Period, the main river flowing through Edo was, in fact, the Tonegawa.

The history of the river is really long and complicated and I don’t want to get bogged down in as much craziness as I did last time with the Sumidagawa. Plus, since most of the Tonegawa is not in Tōkyō, it’s beyond the scope of this blog. Just know that from the earliest records, the Tonegawa had a reputation for periodic horrible flooding and changing course over the years. As such, it was sort of the bad boy of Japanese rivers and was considered untamable. But that didn’t stop people from trying to tame it. Through all of recorded history, there are references to various building projects at various points along the river attempting to calm the raging river.

The headwaters of the Tonegawa.
The Tone River emptying into the sea in Chiba Prefecture.

As mentioned earlier, today the river empties into the Pacific Ocean in present day Chiba. But in the Edo Period the river did not empty out there. In those days it bifurcated into 2 rivers flowing south and east in 怒藩 Oshi Han Oshi Domain in present day Gyōda, Saitama[iii] at a place which is still known today at 会之川 Ai no Kawa, literally, the meeting of the rivers[iv]. The bifurcation doesn’t exist anymore but today the remains of one river is a southeast flowing waterway today called 大落古利根川 Ōtoshi Furu-tonegawa literally the Old Tonegawa Big Drainage Channel. Though not connected today, this “Old Tonegawa[v]” eventually met at a confluence north of Edo where the Arakawa and Irumagawa, and all 3 rivers flowed happily ever after into Edo Bay in a complex alluvial patchwork.

That is until Tokugawa Ieyasu began delegating urban planning and development tasks to various daimyō as part of their sankin-kōtai service. As I mentioned in my last article, one of the daimyō tapped for carrying out river work, was one 松平忠吉 Matsudaira Tadayoshi[vi]. This dude was actually the 4th son of Ieyasu and the lord of 忍藩 Oshi Han Oshi Domain which is now present Gyōda, Saitama[vii].

Reconstruction of Oshi Castle in Gyoda. It’s actually rebuilt in the wrong location. The castle’s honmaru (main keep) is now an elementary school. But many areas of this sleepy, farming town retain place names referencing the castle.

As it turns out, the lord of Tatebayashi at the time[viii], one 秋元 長朝 Akimoto Nagatomo also worked on these flood control projects. 伊奈 忠次 Ina Tadatsugu lord of 小室藩 Komura Han Komura Domain (present day 北足立郡 Kita Adachi-gun North Adachi District, Saitama) was also asked to help out. The lord of  総社藩 Sōja Han Sōja Domain located in present day 前橋 Maebashi in Gun’ma Prefecture was also called upon to implement development of the river path.

Initially, I didn’t know why Matsudaira Tadayoshi was asked to work on this particular project (and the Sumidagawa), but if I had to guess it would be because the lords of Oshi Domain were already trying to temper and control the Tonegawa in their own domain at Ai no Kawa. But seeing the daimyō from Sōja, Tatebayashi, Oshi, and Komura in that order got me thinking. Perhaps it was because they all lived in territories through which the river flowed. As such, they already had experience dealing with this river, or by the thinking of the time, they “owned” responsibility of the Tonegawa – ie; since the major confluence that ran to Edo Bay started in and ran through their respective territories so it was their mess to clean up. That’s just my speculation, but that’s definitely something to think about[ix].

The Tone River as it flows throw Maebashi (present day Gunma Prefecture).

A Quick Note About the Establishment of Edo as a Capital City

What differentiates Ieyasu from the other 武将 bushō warlords before him – and indeed about the other shōgunates before him – is that more than being a general, he had a vision of governance and urban planning[x]. He also had enough kids to ensure proper dynastic succession[xi]. His plans were executed so much better than those of the Kamakura or Ashikaga shōgunates. In my humble opinion, the success of the 徳川幕府 Tokugawa Bakufu Tokugawa Shōgunate doesn’t lie in the fact that Ieyasu became shōgun. It all lays in the fact that Ieyasu set up a tactical administration of the realm that brought everyone into compliance with his system and that his subordinate daimyō actually obeyed his edicts.

Wikipedia actually lists 4 reasons Ieyasu and the shōgunate put such a high priority on taming the Tonegawa. It’s actually an interesting list:

1 – Protect Edo Castle and the administrative centers of government from floods. Also, protect the administrative centers of the domains that existed along the river[xii].

2 – Promote the development of new rice paddies and fields and protect them from flooding. Remember “rice” = “money” in the Edo Period economy. Also a stable economy and a stable farming class meant peace.

3 – Ieyasu, a military general, knew the tactical importance of a good highway system on land and a predictable, traversable network of rivers. Beyond military use, investing in a solid infrastructure that united the domains and brought goods, services, and resources in and out of the capital city was seen as a high priority.

4 – The last one is interesting if you love the Sengoku Period and/or Edo Castle. Apparently, the 伊達氏 Date-shi/Idate-shi Date clan who controlled 仙台藩 Sendai Han Sendai Domain were still perceived as a potential enemy[xiii]. The shōgunate decided to cut off a portion of the Tonegawa to build the 外堀 sotobori outter moat of Edo Castle as an outer perimeter defense in case the Date decided to attack. They didn’t. But the result was a functional, secondary outer moat around the castle and the Tonegawa was diverted east towards present day Chiba.

Map of rivers in the 16th century. The Tone River clearly flows down into Edo Bay.

Building a castle town in an alluvial plain, Ieyasu and his advisers had a myriad of concerns about the rivers. First of all, while his castle was probably immune from serious flooding, his vassals also had to be put into the 山手 yamanote on the tops of hills. Commoners (my shorthand for non-samurai) were in the 下町 shitamachi low ground that constantly flooded – unarguably the worst place to live, because more often than not it meant you lived in a flood plain or potential tsumani zone.

While all rivers were prone to flood, since the Heian Period we have records of the Tonegawa flooding violently. It also looks like the river naturally changed direction many times throughout history. As I mentioned earlier, due to its volatile nature, the people who lived along it were constantly trying to tame the river by whatever means they had at their disposal. The shōgun’s capital, in addition to averaging 1 major conflagration every 6-8 years, was also prone to flooding. Fires in a wooden city are pretty hard to prevent, but controlling rivers is apparently a little easier[xiv].

I could detail each and every change to the river from the Edo Period until recent years, but that would just get boring after a while. Although, in the Edo Period, the river emptied out into Edo Bay where the present day 江戸川 Edogawa Edo River flows into Tōkyō Bay, the end result is that the river was diverted east – and in much the same way as the Sumidagawa was created out of nothing, the Tonegawa was sent out of Edo. It now flows into a former tributary that takes the river into former 下総国 Shimōsa no Kuni Shimōsa Province which is more or less modern Chiba Prefecture[xv].

In 1910, a typhoon caused most of Tokyo’s rivers to flood including the Sumida and Kanda Rivers. Pretty much all of the shitamachi areas were flooded for 3-10 days (depending on sea level elevation).
I’m told this picture is Asakusa.
This kind of flooding rarely occurs in Tokyo since the 1960’s,
Why doesn’t Tokyo flood anymore? This is why. There are massive underground drainage tanks (like this) that fill up with flood water and then pump it out to the sea.

Hey, Marky. You Haven’t Said Anything About Etymology Yet…

Oh, sorry. You’re right. And after all, that’s why we’re all here, isn’t it? Well, the river name is quite old. You’ve already heard me mention the Heian Period, but of course, the river has been here much, much longer. As you can imagine, there are multiple conjectures about where the name comes from. Also, let’s be aware that the old sections of the Tonegawa have the nickname 坂東太郎 Bandō Tarō (Bandō is a pre-modern alternate for Kantō; Tarō is a name or suffix for a the eldest son, in this case it means “the oldest son of Japanese rivers” or is just a sign of affection or endearment).

Let’s Look at the Kanji





This kanji use is ateji, that is to say, the kanji are not used for their ideographic meaning, but rather for their phonetic qualities. The first kanji, is rarely read as /to/ in Modern Japanese. The second kanji occurs in many ancient place names. The combination of kanji would normally be read as 利根 rikon which is an obscure term that means “cleverness” or “innate intelligence.”

Despite its wild and unruly reputation, some stretches of the Tone River seem quite beautiful.

The Ainu Did It.

Of course they did. And there’s no way to prove them wrong (lol). Well, there isn’t, but of course I’m being a little facetious here. Anyhoo, this theory assumes the word is derived from アイヌ語 Ainugo the Ainu language. The word in question is トンナイ ton’nai which in the Kantō dialects could easily be reduced to トンネェ ton’nēトネェ tonēトネ tone. In the Ainu language, ton’nai means “giant valley” and is said to refer to either the Tonegawa river basin or some valley that it flows through. Unfortunately for us, we don’t know what valley that is, so let’s chuck this one up to way out there speculation and impossible to confirm.

Another theory states that it comes from another old Ainu word トンナイ ton’nai which meant a swampy, lakey, wide river, which the Tonegawa most definitely was. As I mentioned before, it’s the largest watershed in Japan and it changed course often. The land received great benefits from river in the form of lakes and swamps, all of which could be used for farming or fishing or, you know, whatever you use lakes for. I dunno, maybe fucking ducks.

The Musashi Waterway in Gyoda, Saitama leads the Tone River towards its confluence with the Arakawa (itself part of the Tone Watershed).

The Mountain Did It.

As I mentioned earlier, the Tonegawa headwaters are at the top of 大水上山 Ōminakami Yama Ōminakami Mountains in 群馬県 Gun’ma Ken Gun’ma Prefecture. This theory states that on the mountain there were many 尖った利き峰 togatta kikimine which translates as something like “dominated by sharp/pointy peaks” or “useful pointy peaks.[xvi]” The idea here is that regardless of kanji the words 尖った togatta sharp and 利 kiki/ri useful were combined. This combination produces a hypothetical form 尖利 toto/tori “sharp + useful” as an abbreviation for the concept that the mountains were either dominated by sharp peaks or useful peaks. From this idea came a later word 利根 tone which literally means the “root/source of usefulness/benefit.”

I don’t think this an impossible etymology, but it is particularly convoluted and requires a lot of back story. Long time readers will know that I’m a big fan of Occam’s Razor and because of that I’m a little skeptical of this theory.

The Ominakami Mountains, source of the Tone River. I guess they do look kinda sharp and pointy.

Some Gods Did It.

This is a really weird theory because it asserts that the river is named after either 等禰直 Tone no Aitai or 椎根津彦 Tone Tsuhiko, two terrestrial 神 kami deities with associations to water shrines that are briefly alluded to in the 日本書紀 Nihon Shoki The Chronicles of Japan and 古事記 Kojiki Record of Ancient Matters, two ancient books telling the Japanese creation myths and legendary foundation stories. I don’t know much more about them.

Tone Tsuhiko. Kind of a boring kami.

The Man’yōshū Did It.

It’s said that the 大水上山 Ōminakami Yama Ōminakami Mountains had the nickname 刀嶺岳, 刀根岳 Tonetake Sword Peak Mountains or Sword Root Mountains, respectively. The nickname was applied to the river and eventually replaced with other kanji because is usually read as // not /to/. Supporters of this theory point out that the earliest reference to the river in the 万葉集 Man’yōshū the Anthology of 10,000 Leaves (8th century) and it was written in ateji as 刀禰 Tone.

As I’ve said time and time again, with really ancient place names written in ateji, there is almost no way of ever recovering the original meaning. The name could predate the spread of the Yamato people, as the Ainu theory suggests, but it could also be much older than that, it is a major watershed so it would have been hard to miss by anyone living near it.
I’m sad to say I can’t point at any of these theories and say “I like this one.” They’re all a little out there and I think the kanji in every case are just afterthoughts. The end.

Support Japan This!

FollowJapan This! on Instagram
Japan This! on Facefook
Japan This! on Twitter
DonateSupport every article on Patreon
Donate BitCoin

Donate via Paypal


ExploreJapan This! Tours


[i] The Shinano flows from Nagano to Niigata.
[ii] For those who don’t know “headwater” means the source of a river.
[iii] “Wait, why are you talking about Saitama?” You may be asking. It ties into Edo, you’ll see.
[iv] Even to this day name applies to where all sorts of vestiges of the Tone Watershed and drainage ditches and irrigation ditches and any kind of waterworks you can imagine keep this rural, farming community supplied with water.
[v] “Old” is a modern label, in its day it was all just part of the Tonegawa, baby.
[vi] Remember, Tokugawa Ieyasu assumed the name Tokugawa. His original family name was Matsudaira. Without going into specifics, the two are more or less equal in meaning.
[vii] Neighboring 館林藩 Tatebayashi Han Tatebayashi Domain, present day Tatebayashi, Gun’ma Prefecture, was also a Tokugawa holding. As mentioned in my article on Hakusan, the 5th shōgun, Tokugawa Tsunayoshi was originally lord of this domain. Although this area is the straight up boonies today with some of the worst weather in the entire country, it is a very fertile agricultural area. Both domains were directly plugged into – by blood – to the 徳川将軍家 Tokugawa Shōgun-ke Tokugawa Shōgun Family. I have family in both towns, and I can assure you that this is a source of pride to some of the local people.
[viii] The Ina clan only held Tatebayashi Domain for a generation or two. Soon a branch of the Matsudaira took it over, but they were eventually superseded by the Tokugawa.
[ix] Or students/scholars, if you’re looking for a thesis topic, there ya go. You’re welcome.
[x] That said, he also had the somewhat stable luxury of being in a position where Nobunaga and Hideyoshi never could have been.
[xi] Something like 11 sons, if I remember correctly. He had a bunch of daughters too, but in the Edo Period women didn’t really count.
[xii] This may be why daimyō considered loyal to the Tokugawa seem to be placed along the river. Hmmmmm.
[xiii] Yes, that Date clan.
[xiv] Don’t get me wrong, Edo flooded frequently. Tōkyō also flooded frequently. These days if floods occur, there are a number of secondary and tertiary contingency plans, including vast underground receptacles that excess water can drain in to. You can actually take free tours of these drainage systems.
[xv] The Tone River now flows past 関宿城 Sekiyado-jō Sekiyado Castle in Chiba. I briefly mentioned the castle in my article on Morishita.
[xvi] I’ve shown this phrase to a few native Japanese speakers and they couldn’t make any sense out of it. It’s nonsense in Modern Japanese. But it is possible to read + as /to ne/) if you want to stretch your imagination.

日本 利根川

3 replies on “The Tone River”

Leave a Reply