Irehara Ruins

A Settlement Born of a Spring

What makes Ireibaru exceptional is its setting. The site rests on gently sloping land that descends from the foot of a low hill toward what was once the seashore, and at its heart lies the spring known as Uchinukā (ウーチヌカー). This natural water source has bubbled up from the earth without ceasing for at least seven millennia — the very reason successive generations chose to live here.

Around the spring, the ancient inhabitants developed an elegantly practical division of space. The damp lowland near the water served as their "kitchen," a place for processing food and storing supplies, while the higher, drier sand-dune zone became the residential quarter where homes and hearths were built. The freshwater from the hills, the marine resources of the nearby reef, and the wild bounty of the surrounding forest all converged at this single, generous spot.

Why This Site Was Designated a National Historic Site

Ireibaru was officially designated a National Historic Site by Japan's Agency for Cultural Affairs on February 22, 2010. The reasons given by experts are as scientific as they are poetic.

First, the site is unique in the entire Nansei (southwestern) island chain in preserving a continuous archaeological record covering all phases of the Jomon period — roughly 4,000 years of unbroken cultural sequence. Nowhere else in southern Japan can researchers trace the rhythms of Jomon life so completely in a single location.

Second, the marshy ground around the spring created waterlogged conditions that preserved organic remains rarely seen elsewhere in Okinawa. Wooden tools, bamboo baskets, seeds, acorns, animal bones, fish bones, and shells survived the centuries here in remarkable condition, allowing scholars to reconstruct daily life and the surrounding paleoenvironment with unusual precision.

Third — and most evocatively — the site has yielded jadeite beads sourced from the Hime River in Niigata Prefecture and obsidian flakes traced to volcanic deposits in Kyushu. These imported materials prove that the people living at Ireibaru thousands of years ago were already part of a vast network connecting Okinawa to the Japanese mainland by sea. The site is, in effect, the southern terminus of a prehistoric trading sphere that stretched the length of the archipelago.

Treasures from the Earth

Excavations conducted between 1997 and 2005 produced a wealth of finds that fill the adjacent Chatan Town Museum. Among the most celebrated discoveries are a wooden basket and the wooden handle of a stone axe — the oldest wooden artifacts ever recovered from any archaeological site in Okinawa Prefecture. A delicate bamboo sieve, used to leach the bitter tannin from acorns of the Okinawan ring-cup oak, ranks among the earliest woven objects in the archipelago. The site also produced the first comb ever found in Okinawa, an unexpectedly intimate glimpse of the people who walked this land.

The pottery assemblage is equally remarkable. Vessels representing nearly every Jomon-period style known in Okinawa have been unearthed here, including Sobata-type ware imported from Kyushu and ceramics whose patterns echo those of distant Tohoku in northern Honshu. Pebble-strewn deposits along the southwestern edge of the site preserve evidence of two ancient tsunami events — one approximately 4,000 years ago and another around 2,000 years ago — quiet reminders that life at Ireibaru was always shaped by the rhythms and risks of the sea.

Highlights for Visitors

The Ireibaru Ruins Park opened to the public on July 1, 2025, and is now arranged as five thematic zones designed to bring the prehistoric landscape back to life. The Jomon Forest area has been replanted with native species such as itajii oak and gajumaru banyan to recreate the satoyama woodland of millennia past. The wetland zone showcases the still-flowing Uchinukā spring alongside a reconstruction of the bamboo storage baskets used to soak acorns. A "marine transgression" zone evokes the ancient shoreline, the sand-dune zone marks the former residential area, and the open lawns invite quiet contemplation of how dramatically the coast has shifted over the centuries.

Sagaribana (powderpuff) trees planted within the wetland have become a beloved feature. Each summer their fragrant blossoms open only at night and fall before sunrise, earning them the nickname "phantom flowers." On select evenings the town hosts a "Jomon Night" event when the trees are illuminated and live music drifts across the ruins — a magical way to encounter the site after dark.

Right beside the ruins stands the Chatan Town Museum, which opened on November 20, 2024. Its permanent exhibition, themed "7,000 Years of Memories," displays the most important artifacts from the site and includes a richly detailed diorama of Jomon-era Chatan. Hands-on workshops — Jomon pottery making, turban-shell ornament crafting, and traditional yushi-tofu preparation among them — turn a museum visit into an active encounter with island heritage.

Around the Site

Chatan today is best known to international visitors as the home of Mihama American Village, a seaside entertainment district where Japanese, Okinawan, and American influences mingle in a riot of shops, cafes, and Ferris-wheel views. From Ireibaru it is only a short drive or pleasant walk away. Sunset Beach, with its famous evening views over the East China Sea, offers an unforgettable end to a day spent among the ruins.

For those drawn to history, Chatan combines well with day trips to Zakimi Castle, a UNESCO World Heritage component of the Ryukyu Kingdom castle ruins, in nearby Yomitan Village. The Okinawa Prefectural Museum in Naha, roughly 30 kilometers south, provides a broader context for the artifacts seen at Chatan Town Museum. Together these stops form a satisfying itinerary that spans tens of thousands of years of island life.