Lapped by the waves of the Atlantic and visible at only low tide, a mysterious rock inscription believed to be centuries old and so far undeciphered lurks outside a French village in Brittany.

The town hall in Plougastel-Daoulas in the Finistere region of Brittany in northwest France is now offering a 2,000-euro ($2,250) reward for anyone who can decrypt the sequence of letters and symbol.

Could the small boulder have been used for a love letter whose secret has remained untouched for centuries, or a proud note left by an eighteenth-century fort-builder? Or something even more mysterious?

French local councillor in charge of small heritage Michel Paugam poses on May 7, 2019 as he shows inscriptions composing indecipherable words on a rock in the Brittany village of Plougastel-Daoulas. – The city launched a national call with a 2000 euros reward to anyone able to solve the mystery of those inscriptions propably made during the 18th century. (Photo by Fred TANNEAU / AFP)

Locally, the rock is sometimes compared to the Rosetta Stone, the great ancient Egyptian stele now in the British Museum whose inscription was partly deciphered by the French Egyptologist Jean-Francois Champollion.

The authorities in Plougastel-Daoulas hope that their competition will shed light on the enigmatic piece of history.

“This inscription is a mystery and it is for this that we are launching the appeal,” said Veronique Martin, who is spearheading the search for a code-cracker.

The rock, which is around the size of a person, is accessed via a path from the hamlet of Illien ar Gwenn just to the north of Corbeau point.

The inscription fills the entirety of one of its sides and is mainly in capital letters but there are also pictures including a sailing boat. There are two dates, 1786 and 1787.

“These dates correspond more or less to the years that various artillery batteries that protected Brest and notably Corbeau Fort which is right next to it,” she said.

On a first glance the inscription defies interpretation.

“ROC AR B… DRE AR GRIO SE EVELOH AR VIRIONES BAOAVEL… R I OBBIIE: BRISBVILAR… FROIK…AL,” read parts.

This picture taken on May 7, 2019 shows inscriptions composing indecipherable words on a rock in the Brittany village of Plougastel-Daoulas. – The city launched a national call with a 2000 euros reward to anyone able to solve the mystery of those inscriptions propably made during the 18th century. (Photo by Fred TANNEAU / AFP)

“There are people who tell us that it’s Basque and others who say it’s old Breton,” said the mayor of Plougastel-Daoulas Dominique Cap.

“But we still have not managed to decipher the text,” the mayor told AFP, adding the rock was first spotted around three-four years ago.

The appeal to crack the code has been made to linguists, historians, academics, students or simply people who enjoy code-breaking as a hobby.

A jury will then meet to choose the most plausible suggestion and award the prize.

“There are a lot of words, they’re letters from our alphabet, but we can’t read them, we can’t make them out,” said the municipal councillor in charge of local heritage Michel Paugam.

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