OTSU, Shiga Prefecture--Authorities are stepping up measures to preserve underwater cultural sites, ranging from medieval Mongolian invasion ships sunk by a “divine wind” to inland ruins now submerged in lakes.

The Agency for Cultural Affairs is working out a manual that will set standards for research and preservation of the underwater sites.

The term “underwater cultural heritage” typically evokes images of such things as shipwrecks carrying valuable cargo. But the concept of underwater cultural heritage has expanded and covers things normally associated with land.

The Agency for Cultural Affairs and other entities organized a February symposium in Otsu titled “State of public administration work on the preservation of underwater ruins II.”

During the conference, Ken Tanaka, a curator with the Murakami Kaizoku Museum, talked about the ruins of Noshima Castle, a stronghold of the eponymous kaizoku (“pirate”) forces that held sway over the Seto Inland Sea during Japan’s Warring States Period (late 15th to late 16th centuries).

The museum in Imabari, Ehime Prefecture, was previously called the Murakami Suigun Museum. (Suigun is Japanese for naval forces.)

Noshima Castle, ruled by the Noshima Murakami clan, is an unorthodox marine castle that fortified both Noshima and Taizakishima islands, which are part of the Geiyo Islands in the Seto Inland Sea.

Four hundred “reef pits” have been found drilled in rock in the intertidal zone along shorelines there. Some holes measure 40 centimeters in diameter while others are 15 to 20 cm. They come in different forms: Some are lone while others are arranged in regular patterns, including a single, horizontal array of smallish holes.

The holes are believed to have held wooden pillars so ships could be moored there. But Tanaka pointed out other possibilities, saying the holes may have been traces of piles for piers and seawalls.

“The reef pits are characteristic of the Geiyo Islands and are likely a common feature of remnants associated with the Murakami Kaizoku,” Tanaka said. “The term ‘castle’ tends to evoke the image of a land or mountain fortress, but an island castle, which straddles both land and sea, should perhaps also be recognized as yet another form of underwater ruins.”

Around 70,000 artifacts have been unearthed at the site, including ceramic pieces of Bizen ware from what is now eastern Okayama Prefecture, as well as pottery and tea ceramics from Korea and China. Although the Murakami Kaizoku is typically viewed as a group of rough fellows, the findings suggest they were also physical distribution workers and culture lovers.

How to preserve the site presents a headache, though.

Waterfront ruins always face the risk of disappearing under the strong impact of tide currents and ship wakes. Tanaka and his colleagues are looking for an effective site-preservation environment.

“What we are doing could serve as a model for the preservation of waterfront ruins,” he said.

Not all underwater cultural heritage sites are located in the sea.
Underwater ruins have been found at 74 sites in Shiga Prefecture’s Lake Biwako, where large-scale development projects began in the 1970s. Many of them were initially above water and were later submerged.

The Tsuzuraozaki lacustrine site beneath the northern part of Lake Biwako has produced earthenware from the early Jomon Pottery Culture Period (c. 14500 B.C.-1000 B.C.) through the Heian Period (794-1185). The southern part of the lake is home to a crowd of archaeological ruins, including the Awazu lacustrine site, according to Isao Iba of the Shiga Prefectural Azuchi Castle Archaeological Museum.

“Underwater heritage sites are testimony to the history of exchanges by sea,” said Toshihide Omi, chief senior specialist for cultural properties with the Agency for Cultural Affairs. “To allow them to be preserved like land-based sites, there is a need to locate those underwater sites and let the public learn about them.”

It is never easy to accurately locate underwater heritage sites even in Japan, which is surrounded by the sea.

A survey conducted by the Agency for Cultural Affairs through local governments found that Japan has 387 underwater archaeological sites. But the statistics likely do not reflect the entire picture, considering Japan has more than 460,000 land-based sites.

Local government officials in charge of public administration work for preservation tend to shy away from underwater archaeological sites because of the difficulties involved in the task.

For that reason, the Agency for Cultural Affairs has set up a study panel of experts and plans to publish a preservation manual in fiscal 2021.

“I hope people will lower their psychological barriers (to underwater sites) for starters,” said panel member Yoshifumi Ikeda, a professor of archaeology with the University of the Ryukyus.

Ikeda has been studying shipwrecks of a Mongolian invasion force that was thwarted by a typhoon off Takashima island in Nagasaki Prefecture in the 13th century.

One of those seabed areas is designated a national “historic site.”