Slowly being enveloped by the tropical jungle, on the island of Kosrae (Micronesia), are the ruins of an enigmatic ancient civilization called Lelu whose relationship with the coral reef is unparalleled in modern day. Known as the ancient capital of the Pacific Ocean, Lelu developed in the six centuries preceding European contact A.D. 1250-1850.

Historical accounts by the French and Russian explorers in the early 1800’s tell us Lelu city was an impressive sight, covering approximately 20ha, containing an extensive canal system and a network of compounds with walls constructed from huge boulders and megalithic basalt prisms arranged in header and stretcher fashion.

Lelu is also features truncated pyramid tombs where kings and high chiefs were buried (Insaru compound). Exactly how the city was engineered including how the basalt megaliths were moved from their distant quarries, over land and water, and erected on site is not known, but local tradition implies Lelu was built using magic.

Zoe at Inaru Twin Tombs
Dr Zoe Richards examining the corals used to construct one of the twin tombs of Insaru (the sacred compund of Lelu). Image: Zoe Richards
© Australian Museum

As a coral biologist, I was fascinated to recently discover that corals were used extensively in the construction of Lelu, and most notably, to build the sacred burial tombs. History tells the coral tombs were temporary processing points and that the royal bones were exhumed from the crypt and secondarily buried in a hole on the nearby Lelu reef.

The total amount of coral used to construct the ancient city would have been enormous because outside of the Insaru compound, coral was used to pave roads, construct compound and canal walls and a seawall that was more than 3 m high and over 1 km long, and in landfill to reclaim over 180,000 m2 of land.

My colleague, Dr Jean-Paul Hobbs and I have just returned from an expedition to Kosrae (funded by the Australian Museum Foundation). With the assistance of Mr Paliknoa Sigrah (Lelu Ruins Association), Mr Berlin Sigrah (Kosrae Preservation Society), Osamu and Marston (Kosrae Conservation and Safety Organisation) and Ben (Kosrae Village Resort) we surveyed which corals were used to construct the sacred tombs.

We also collected coral samples from three tombs in order to obtain precise dates using advanced radiocarbon dating analyse (Th/U).

Collecting corals from Insaru Tomb 3.
Ben and Zoe collecting corals from Insaru Tomb 3. Image: Zoe Richards
© Australian Museum

Today, the Lelu ruins are globally significant because they hold important information about the customs and structure of the ancient Kosraen civilization prior to European contact. These ruins also have the dual function of providing the opportunity to study historic ecology and paleoclimatology.

The local community are dedicated to safeguarding the ancient ruins and ensuring future generations learn about their unique cultural history.

This research project was funded by the Australian Museum Foundation.