In what is arguably the greatest cold case in history, archaeologists in Athens are trying to decipher the mystery of two mass graves discovered in the seaside suburb of Faliro, on the construction site of the new architectural complex that will host both the National Library of Greece and the National Opera.

Work on the site revealed an ancient cemetery of significant archaeological value, an extension to the necropolis (burial ground). The broader region has been excavated for more than a century, but the discovery of two mass graves is of specific interest, shedding light to one of Athens’ darkest periods. According to Stella Chryssoulaki, the regional archaeological services director, the skeletons of 80 men found in the grave may have been the followers of ancient would-be tyrant Cylon of Athens.

The theory is corroborated by other findings: two small vases discovered among the skeletons have allowed archaeologists to date the graves from between 675 and 650BC, a period of great political turmoil in the region; Cylon’s failed coup to rule Athens is detailed in the writings of Herodotus and Thucydides that describe the path that led to the establishment of democracy after years of aristocracy and tyranny. A nobleman and former Olympic champion, Cylon aspired to become a tyrant of Athens, but Athenians opposed the attempted coup, urging him and his supporters to seek refuge in the Acropolis. The conspirators eventually surrendered after winning guarantees that their lives would be spared, but in an act of sacrilege, Megacles, of the powerful Alcmaeonid clan, had the men massacred.

Now archaeologists claim that their remains have been found, as AFP reports. The skeletons were found lined up, some on their backs and others on their stomachs. A total of 36 had their hands bound with iron. All this is presented as proof of the status of the buried as prisoners, according to archaeologists.

Given “the high importance of these discoveries”, the Central Archaeological Council is launching further investigations, the culture ministry of Greece said in a statement.