筑後川をたどる：大分から佐賀へFollowing the Chikugo River from Oita to Saga

Today I departed from Oita City, passed through Hita City and Ukiha City, reached the Ariake Sea, and then arrived in Saga. One of the purposes for choosing this route was to focus on the Chikugo River. The Chikugo River originates from Mount Aso and flows east to west across four prefectures in northern Kyushu—Kumamoto, Oita, Fukuoka, and Saga—before emptying into the Ariake Sea. I traveled along the Chikugo River down to the Ariake Sea, and the first place I visited was Hita City, a basin at the entrance of the mountains, which can be called a strategic point of this river.

Although Hita City hardly draws attention today, historically it held extremely important significance, particularly during the Edo period, when it became a directly governed land of the shogunate, known as tenryo (天領). The reason was that Hita City was a transportation hub from which roads and rivers radiated across Kyushu—northward to Fukuoka, eastward to Oita, southward to Miyazaki and Kagoshima, and westward to Saga and Nagasaki. It was known from ancient times as the Hita road (Hita Kaido, 日田街道), a route where people, goods, and information frequently passed. Especially during the Edo period, because Kyushu was the region farthest from Edo, the Tokugawa capital, it was difficult to monitor, and thus Hita was made a shogunate-administered territory to serve as a base for surveillance and to prevent uprisings.

However, it was not the Tokugawa who first recognized the importance of Hita. Remarkably, traces show that from the Yayoi to the Kofun periods, this area was already regarded as significant and underwent development. Why then did this region, which today hardly stands out, attract people from ancient times? One reason lies in its position as a junction with maritime transport. In fact, the Mikuma River (the local name of the Chikugo River in this region), which flows right by Hita, is the main stream of the Chikugo River, and if one travels about 75 kilometers downstream from there, one reaches the Ariake Sea. Many kofun (ancient burial mounds) and settlement remains have been found around Hita, suggesting that it was deeply connected with the activities of ancient maritime clans.

For a long time, it has been assumed that immigrant clans who came to Japan entered the Genkai Sea via the Korean Peninsula and Tsushima, landed in northern Kyushu, and then moved south. However, by tracing the Chikugo River on this journey, another route has come into view—one not from the Genkai Sea but from the Ariake Sea, ascending inland along the river. The old traces of this route remain in the arrangement of shrines along the Chikugo River and in the nature of their enshrined kami, showing that maritime clans had long been deeply involved in this river basin. For example, in Hita City on the Mikuma River, the custom of cormorant fishing is handed down, but despite being on a river, sea cormorants are used instead of river cormorants. This clearly reflects the influence of ancient maritime clans on river basin culture.

Hita preserves archaeological sites such as large round kofun resembling UFOs, but moving west into the area around Ukiha in Fukuoka Prefecture, one finds that the local belief systems show strong Izumo influences, intertwined with maritime clan faith. Many shrines along the Chikugo River enshrine kami connected with Izumo, suggesting traces of Izumo people having once migrated or expanded into this region.

Here one must take into account the myth of kuni yuzuri (国譲り), the transfer of the land. This derives from the tale that Okuninushi, the kami of present-day Izumo Taisha who ruled a vast sphere of influence led by Izumo, was required to cede the land to the newly emerged faction of Amaterasu. Although the myths do not describe what happened afterward, it is highly possible that following the transfer of the land, the Izumo people, having lost their hegemony, dispersed to various regions. This is not merely speculation; evidence lies in place names across Japan, in ancient records, in shrine deities, and in local traditions, all of which suggest that this was a great event that was both mythological and historical.

Moreover, Okuninushi, enshrined at Izumo Taisha, is the “Great Master of the Land,” equivalent to an ancient powerful ruler who unified a federation of clans. Okuninushi also made alliances through marriage, subjugating clans across the country. It may be that the remnants of Izumo faith along the Chikugo River, when traced back to their origin, indicate that Izumo power had ties with various parts of Kyushu or that they represent memories of people dispersed after the kuni yuzuri.

From this perspective, it becomes increasingly important to consider not only the traditional Genkai Sea route but also the route ascending the Chikugo River from the Ariake Sea. This is because, as is evident from the way Hita functioned as a hub from which roads extended radially across Kyushu, controlling this place meant, ultimately, controlling Kyushu—not only for the Edo shogunate but likely for rulers of earlier times as well.

Above all, if we focus on the movements of maritime clans, ascending the Chikugo River from the Ariake Sea to Hita would have opened routes utilizing other rivers to reach Oita City, and further to Beppu and the southern part of the Kunisaki Peninsula. This suggests that it was one of the main routes of ancient times. As I mentioned previously, even in the traditions of Usa Jingu—one of the most highly revered shrines in Japan—the mysterious kami Hime-Okami is said not to have landed directly at Usa, but rather first at Nata-no-Miya on the southeastern side of the Kunisaki Peninsula.

Today, Hime-Okami of Usa Jingu is explained as being connected with the three Munakata goddesses worshipped by maritime clans of Munakata City in Fukuoka Prefecture (Genkai Sea). But to put it plainly, this is a later revision. The deeper stratum points instead to goddess worship originating from the Ariake Sea, not the Genkai Sea. Taken together, these facts reveal that there existed an ancient route advancing inland from the Ariake Sea along the Chikugo River and then across to Oita, with Hita and Ukiha as its strategic nodes, suggesting that this region may have held considerable importance before the Yamato polity and the history of emperors even began.