Zakynthos

Divers had found what appears to be paved floors, courtyards and column bases. However, no other evidence of antiquities exist at this site. Instead, scientists from the University of East Anglia and the University of Athens considered the possibility of geological origin.

Lead author Prof Julian Andrews said: "The site was discovered by snorkellers and first thought to be an ancient city port, lost to the sea. There were what superficially looked like circular column bases, and paved floors. But mysteriously no other signs of life – such as pottery.

"The disk and doughnut morphology, which looked a bit like circular column bases, is typical of mineralization at hydrocarbon seeps – seen both in modern seafloor and palaeo settings."