Seventh century Japan wasn’t yet a nation-state, but neither were any of its Asian neighbors. Nonetheless, the most powerful of the various groups on the Japanese archipelago, the Yamato, had regular trade and cultural exchanges with its counterparts on the Korean Peninsula, especially the kingdom of Baekche (southwestern quadrant of the peninsula). So when the Baekche kingdom was threatened by an alliance of the Shilla kingdom (its neighbor to the east) and Tang China, the Yamato were ready to come to the aid of the Baekche.

Between 661 and 663 this included sending several fleets carrying commanders, soldiers, and weapons. The exact number cannot be known (what records exist are inconsistent), but it must have been a substantial number, given that at the 663 Battle of Paekchon River (known in Japan as the Battle of Hakusukinoe) 400 ships were lost together with 10,000 men (according to Chinese records). It is said the Yamato fleet was caught in a narrow part of the river from which they could not escape.

Having suffered such a crippling defeat (said to be the worst defeat ever suffered by Japanese troops), the Yamato quickly retreated back to their archipelago, together with hundreds of Baekche refugees, their kingdom have been effectively annihilated by the Chinese-Shilla alliance.

Even with the Tsushima Stait as a protective water barrier, after their defeat the Yamato felt themselves vulnerable to attack. The emperor deployed refugee Baekche generals to help construct defenses, especially in northern Kyushu, the part of Japan closest to Korea. The result was several mountain fortresses where weapons and supplies could be held in reserve for troops in case of attack. The mountaintop locations also enable the various fortresses to communicate through signal fires.

One such fortress, on a Kumamoto mountaintop in Yamaga city, is being excavated and turned into a 55 hectare historical park. So far, the foundations of 72 structures have been uncovered across the broad mountaintop, including two octagonal towers, several storehouses, troop barracks, and administrative buildings. Further down the steep slope are a water catchment area and the remnants of earthen ramparts broken occasionally by narrow gates perfect for defense against would-be invaders.

In order to bring this ancient history to life, some buildings have been reconstructed, with others planned for the future. The locations of foundation stones of various unreconstructed buildings dot the site.

Perhaps most distinctive is the reconstructed octagonal drum tower. Drums would have been used to send messages to anyone within hearing distance. Archeologists could readily discern the octagonal shape of the building from the orientation of the foundation stones, as a nearby replica clearly shows. Peak inside to see how the pillars held up the tall tower, an impressive site even today but all the more so 1,300 years ago.

Structures of this shape and design are very unusual in Japan; but similar buildings are found in Korea, further evidence that the fortress was designed and built by Korean generals transplanted after the Battle of Paekchon River. There are at least four such “castles” in northern Kyushu. Known as Chosenshiki (Korean-style) castles, they are Kaneda Castle on Tsushima island in Nagasaki, Ono Castle in Fukuoka, Kii Castle in Saga, and Kikuchi Castle. All of them were intended to protect the governmental administrative center of Dazaifu, which became the single gateway to the archipelago for the next few centuries. Indeed the centralization created by this perceived need for defense had, within a few decades, even resulted in a change of name for the islands, which now became known in Asia as the “land of the rising sun”, or Nihon (which in English becomes Japan).

Other reconstructed buildings include storehouses for foodstuffs and weaponry. Storehouses are easily identified because they were built on stilts to keep their contents dry. Various kinds of barriers were used on granaries to keep vermin out as well. Look closely at the tile-roofed granary in the foreground below–there is a diagonally-cut beam running across the tops of the stilts, thought to be impossible for mice to surmount. The thatch-roofed storehouse is believed to replicate an armory.

Troop barracks have also been reconstructed based on foundation stones, although they bear a surprising resemblance to their modern counterparts. Foundations uncovered behind the barracks are believed to have been more salubrious accommodation for use by officers or administrative personnel. Perhaps someday they, too, will be reconstructed.

Visitors can follow pathways down the hillside to the sites of three of the castle’s former gates; a chance to inspect the just how narrow the apertures were and how difficult attack would have been. There are also a couple of lookout points from which to look out at the entire valley below.

Near the park’s entrance is a concession area and a visitor center with displays of various artifacts that have been uncovered at the site, as well as dioramas and other simulations. There is even a short video (with English subtitles) to introduce the site. The docents are friendly and eager to help visitors understand this fascinating bit of history. The visitor center is open 9:30-17:15; closed on Mondays.

In the end, the feared invasion never came and the defenses were never necessary. The Tang Chinese and the Shilla turned on each other and their alliance disintegrated, leaving the Korean Peninsula to sort out its own way, with the Japanese somewhat hesitant to move beyond trade for the next several centuries. At the same time, it appears from historical records that the fortress at Kikuchi continued to be occupied for around two centuries.

The remote mountain fortress is most easily reached by private car, but it is also possible to take the Sakuramachi Bus from Kumamoto Bus Terminal to Kikuchi Plaza and get a local taxi for the 5 minute ride to the castle.

(If you want to learn more about this period of Japan’s history, I can recommend Gateway to Japan: Hakata in War and Peace, 500-1300 by Bruce Lloyd Batten (2006). Very readable history.)

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