徳島の古代海人：海部氏と長国の遺産Ancient Seafarers of Tokushima

Today I am in Kaiyo Town, located on the southern coast of Tokushima Prefecture facing the Pacific Ocean. Kaiyo Town was established in 2006 through the merger of three towns, and the area I visited was formerly known as Kainan, with traces of that name still visible on signs throughout the region. The most famous site in this area is the cave at Cape Muroto in Kochi Prefecture, where it is said that Kukai, who opened the Shikoku pilgrimage, attained enlightenment. Yet Kaiyo, located about 50 kilometers north along the coast from there, is a remarkable region with roots far older than Kukai.

The reason I came here is because this is an indispensable region for understanding the traces of the ancient seafarers (ama) who once wielded great power traveling across the seas. This heritage remains in the place name of Kaifu District (海部郡) in present-day Tokushima Prefecture. The reading of “海部” has varied—commonly read as "Ama,"“Amabe,” but in this area it is uniquely read as “Kaifu.” According to folklore studies, however, its origin is thought to lie in “Amabe” (海部).

The origins of these people are uncertain, but this southern region was historically distinguished from the northern Yoshinogawa basin, which was the center of the ancient land known as Awa-no-kuni (阿波国). The southern half maintained its own independent power, referred to as Naga-no-kuni (長国). In fact, traveling southward along the coast from Tokushima City toward Kainan, one encounters numerous place names that retain the resonance of ancient languages. Examples include 「那賀／Naka」「日和佐／Hiwasa」「阿南／Anan」「牟岐／Mugi」「宍喰／Shishikui」「那佐／Nasa」.

These distinct names, with their unusual but beautiful sounds, may sound strange to the ear today, but they are thought to derive from the language of the ancient seafarers. This stands as evidence that the Kaifu clan (海部氏) once held sway over this area, for what ultimately remains over time is language and place names—cultural traces without physical form.

As I write while gazing at the Kaifu River (海部川), which flows into the Pacific at Kainan, I recall that along its banks once stood the stronghold of the Kaifu clan in the Sengoku period. On the hillsides near the river, there are remains of ancient castles, from which one can look out over the entire Pacific coast, toward Anan, and even back to the towering, rugged peak of Mt. Tsurugi. This location, since ancient times, was ideal for monitoring any movements of the Awa forces advancing south from Mt. Tsurugi or visitors arriving by sea. Long before the Sengoku period, however, the ancient seafarers established their base on a smaller hill slightly further south.

Although now depopulated and overgrown, appearing left behind by time, this region was home to people who appear even in the earliest Japanese historical records. One of these is the Wei Zhi Wo Ren Den (魏志倭人伝), a Chinese chronicle recording the journey to meet Queen Himiko of Yamato. The positions of the countries it names remain unclear, with scholars offering divergent interpretations. Yet by focusing on surviving place names and cultural traces, it is highly plausible that one of these countries refers to the Kainan region.

Climbing the hill believed to be the old base of the Kaifu clan, one can overlook Ajironozaki Cape, Dejima, Ozushima, and Tsushima. If ancient seafarers occupied this site, they must have posed a formidable gateway to others traveling on the Kuroshio Current. The wide coast stretching below, backed by ridges fading into the distance, evokes a familiar landscape—Kumano. From the Kumano-nada coast at Shingu in southern Wakayama Prefecture, the view of the Kii mountain ridges bears a striking resemblance to that of Kainan. Since one could travel between Kainan and Shingu by sea, the two areas may have been closely connected.

Tokushima also has scattered burial mounds, and on the Awa side zenpo-koen-fun (前方後円墳), directly linked to the Yamato court, had been confirmed. But in the Kaifu District, including Kainan, none had been found, which is why historical attention has long focused only on Awa. Nagano-kuni was dismissed as a region without strong rulership.

However, in autumn 2023, during pre-construction surveys for a highway, multiple burial mounds were discovered atop a hill in Kainan, including a zenpo-koen-fun. Despite this, perhaps due to the long neglect of Nagano-kuni in historical discourse, preservation efforts have been weak, and debates continue. Some burial mounds may even be destroyed. If proper investigation and preservation were carried out, it would necessitate a reevaluation of the relationship between the Kaifu clan and the Yamato court, providing a counterpoint to the neglect of maritime activity in conventional ancient Japanese history. In fact, such findings could demand a comprehensive reassessment of Japanese antiquity as a whole. Concerned that these sites may soon be destroyed by construction, I climbed the animal trails today to see the hilltop myself.

More realistically, another crucial factor when considering this region is the Nankai Trough megathrust earthquakes. The southern coast of Shikoku has long been repeatedly struck by earthquakes and tsunamis generated by the Nankai Trough, wiping out entire villages. Indeed, along the coast are many stone monuments recording the inundation points of tsunamis from the Edo and Showa periods, warning future generations not to live seaward of them. These stones endure for centuries and remain effective means of transmitting knowledge. Yet when the next great earthquake comes, the calm sea before me could instantly transform into towering waves, once again sweeping away culture and traces of the past into the ocean. In a sense, history and culture return to the sea, and it is within this cycle that human life has been sustained.

For this reason, I am considering multiple approaches for prioritizing research. But if a Nankai Trough megathrust earthquake strikes and this region is devastated, discussions about the ancient seafarers of Japan may be delayed even further, and we could lose forever the opportunity to uncover their history.