Maehata Ruins

An Ancient Earthwork on the Frontier of Dazaifu

The Maehata Site sits on a low ridge in the southern part of Chikushino City, Fukuoka Prefecture, where archaeologists uncovered something rarely preserved so clearly: a long artificial bank of packed earth raised more than 1,300 years ago. In March 2025 it became Japan's newest National Historic Site, recognized for what it reveals about how the early state defended its southern frontier.

The structure is what specialists call a doruijō ikō, an earthwork-like feature. It runs north to south along the spine of a hill extending east from the Sefuri Mountains, following the natural ridgeline rather than crossing flat ground. Excavators traced it for at least 558 meters in broken stretches, and the designated portion covers roughly 320 meters. At its base the bank measures 14 to 15 meters across, and the surviving earth still rises 2.5 to 3.5 meters in two stacked tiers.

Why Anyone Built It: The Year 663 and Its Aftermath

To understand the bank, look back to 663. A Japanese fleet sent to aid the Korean kingdom of Baekje was crushed by combined Tang and Silla forces at the Battle of Baekgang, known in Japanese as Hakusukinoe. The defeat sent a shock through the Yamato court, which now faced the prospect of invasion from the continent.

Over the following decades the government concentrated resources on fortifying northern Kyushu, the region closest to the mainland and the likeliest path of any attack. The center of that effort was Dazaifu, the regional office that managed civil administration, military affairs, and diplomacy for all of Kyushu. Around it rose a ring of defenses: the long water-filled rampart of Mizuki, and the mountain fortresses of Ōno Castle and Kii Castle, built partly with engineering brought by refugees from Baekje. The Maehata earthwork lies about seven kilometers southeast of the Dazaifu government seat, on the line linking Kii Castle with the fortress of Ashiki.

What Earned It National Recognition

What set the Maehata earthwork apart during study was how it was made. The builders shaped the ground first, in places carving it into steps, in others leveling it, then raised the bank by laying thin alternating layers of different soils and tamping each one firm. This rammed-earth method, called hanchiku, appears in ancient ramparts and castle walls across East Asia.

Yet some of the techniques recorded at Maehata have not been found at any other earthwork in Japan. The variety suggests that the engineering knowledge reaching the islands in this period was not uniform, and that several building traditions were in use at once.

The sheer scale points to organized, state-level labor rather than a local undertaking. Set among Mizuki, Ōno Castle, Kii Castle, Ashiki Castle, and smaller earthworks such as Sekiya and Tōregi, the find raises the possibility that an outer defensive line shielded Dazaifu over a far wider area than scholars had mapped. For the question of how that line was planned, Maehata is now a key piece of evidence.

Reading the Bank: What the Excavation Showed

Two graves helped fix the dates. On the hilltop just east of the bank, archaeologists found a small round burial mound from the mid-7th century. About four meters east of the surviving earthwork, where the bank would once have continued, lay a pit grave from the late 9th century. Together they bracket the span when the structure stood and functioned. City records describe it as built around the mid-7th century and chiefly in use through the late 8th century, while the national register gives a longer range reaching the late 9th.

For anyone who studies earthworks, the most telling record from Maehata is the cross-section. Where excavators cut through the bank, the layered bands of packed soil appear as clean stripes, the signature of careful, deliberate construction. Photographs of these trench walls, released by the city, convey the labor far better than the grassed-over ridge visible on the surface today.

Planning a Visit, and Where to Go Instead

One thing to settle before any trip: the Maehata Site is not open to visitors. Part of it lies on private land, and the city has not arranged access or on-site guidance. There is no marked trail, viewing platform, or signage at present.

What you can do is explore the wider landscape the earthwork belonged to. The Chikushino City History Museum holds the excavation reports and the materials prepared for the designation, and makes the best starting point for understanding the find. A short way north, the related defenses of old Dazaifu are open and rewarding. The Mizuki rampart still crosses the valley as a tree-covered embankment. The stone-walled ruins of Ōno Castle crown Mount Shiōji above the government office site. Kii Castle straddles the Fukuoka–Saga prefectural border. The Dazaifu government office ruins themselves, a broad field of foundation stones, anchor the whole region.