海部をたどる：大分沿岸の古代海洋部族Following the Amabe: Ancient Seafaring Tribes of the Oita Coast

Today I am traveling along the coastal region of Oita Prefecture while researching the Amabe (海部), considered to be one of the largest ancient maritime clans. Although most of their traces have been lost today, in ancient Japan they were indispensable in the transmission of people, goods, and information, playing a crucial role in people’s lives and in the structures of power. The Amabe were closely related to the Kaifu clan (海部氏)that I recently studied in Tokushima Prefecture, but since this region was once called Bungo Province, they are positioned as the Bungo Amabe. By tracing these maritime clans that lived across the sea from each other in Bungo and Shikoku, we can pursue the traces of history that have been swallowed by the sea of ancient Japan.

Among them, one of the most important strongholds of the Bungo Amabe is the Kamezuka Kofun in the eastern part of Oita City. The Kamezuka Kofun is a massive keyhole-shaped tomb (前方後円墳) about 116 meters long, constructed on a hilltop plateau with a commanding view of Yamaguchi Prefecture and Shikoku. It is an enormous and imposing keyhole-shaped tomb, and according to the Bungo no Kuni Fudoki (豊後国風土記), this entire area was once called Amabe District (海部郡).

Another important site is the Tsukiyama Kofun, located in the present-day Kanzaki Village area of Oita City. In 1932, during excavation for shrine construction by local people, two ancient stone coffins were discovered. The kofun is about 90 meters in length, and is estimated to have been built in the mid-5th century. It is now known as the oldest keyhole-shaped tomb in the region. Four burials were found—two male, one female, and one unidentified—along with grave goods such as magatama beads and weapons. In addition, 16 kofun are clustered in the Kanzaki Babajo district, indicating the presence of a powerful ruling force in the region.

Particularly noteworthy is the female skeleton buried at the central southern position within the Tsukiyama Kofun. This individual was likely the chieftain, the central figure of the local clan, suggesting that the Bungo Amabe may have been led by a female ruler. Furthermore, among the grave goods were items that suggest trade connections with the Amami and Ryukyu Islands to the south. This implies that the ancient Bungo Amabe played a role in a maritime trade network linking Kyushu with Amami and Ryukyu, showing that they had extensive connections. Such exchanges unique to maritime clans are deeply linked to later Amami and Ryukyu myths, as well as southern island cultures, and are extremely important in understanding the spread of sea people culture across the Japanese archipelago.

Thus, the Kamezuka Kofun and Tsukiyama Kofun demonstrate that the Bungo Amabe controlled wide-ranging maritime routes and engaged in exchanges with the south even before the establishment of the Yamato court. Their presence was not limited to being a regional clan, but rather, they played a central role in the maritime networks of ancient Japanese history.

The area surrounding these kofun clearly shows that the Bungo maritime clans once dominated the sea and prospered greatly, and their relationship with neighboring Shikoku cannot be overlooked. Of particular importance is the fact that this sea area is called the Bungo Channel (豊後水道), which includes the Hayasui Seto (速吸瀬戸), also known as the Hoyo Strait (豊予海峡). The name “Hayasui” points to the goddess Hayasui-hime, who appears in Japanese mythology and plays an important role in its narratives. At Cape Saganoseki, facing the Hayasui Strait, the Hayasui-hime Shrine (早吸日女神社) was established.

The Hayasui-hime Shrine enshrines a deity known as Otsuchi Onabara Moromoro no Kami (大地海原諸神), a rare kami that was originally a natural deity worshipped by those who ventured out to sea in ancient times. This deity was later deified as Hayasui-hime and became an object of worship. It follows that priestesses, who were also the leaders of the Amabe, conducted rituals to calm the kami of the perilous Hayasui Strait so that no disasters would occur, enabling the clans to navigate the Bungo Channel safely.

According to mythological tradition, when Emperor Jimmu (神武天皇)embarked on his eastward expedition to Yamato, as he passed through the Hayasui Strait, local women of the sea received a sacred sword from a giant octopus dwelling on the sea floor, a sword that calmed the tides, and presented it to Jimmu, allowing him to cross the dangerous strait safely. This story conveys a union of natural faith and practical seafaring needs.

Continuing southward along the Oita coast past the Hayasui Strait, one eventually arrives at the Motonoma Strait near fishing villages in Saiki City. Here lies a breathtaking viewpoint toward Oshima Island, with a panoramic view stretching from Uwajima in Shikoku to Cape Sada. Oshima lies in the middle, with northern Oita visible to the left, making it an ideal location for the Bungo Amabe. Establishing bases in such strategic places with expansive views, those who ruled the sea used the mountains at their back as natural fortresses to expand their power.

By steadily securing these maritime choke points, and through the unifying role of priestess rituals that bound together practical trade and spiritual belief, the Amabe became too significant to be ignored by the Yamato court and eventually appeared in historical records as “Amabe.” Later, a new clan called the Azumi clan (阿曇氏)emerged to unite the various Amabe, with their stronghold located on Shika Island in Fukuoka Prefecture.

As I gaze at the swirling currents and the fishing boats returning south at sunset, I cannot help but feel that in this strait between Oshima and the mainland, countless people of diverse cultures once passed through, and that our ancestors too must have crossed these same dangerous waters, becoming part of our lineage.

In Japanese history, many ancient clans disappeared over time, but even driving through this region today, I feel increasingly as though I am wandering into a foreign land, losing sense of where I am, entering a kind of trance. Perhaps this is exactly like the legend of Urashima Taro, who was guided by a turtle to the Dragon Palace (竜宮城)beyond the sea. I once wrote that crossing a single mountain in Japan meant entering another world, but through this journey I strongly feel that the same truth applies to the sea.