Legends of lost cities hiding underneath the seas never cease to enrapture people. Whether it’s the city of Atlantis, likely inspired by the cataclysmic eruption at Santorini, or the mythical Kitezh, said to be hiding beneath the waters of Lake Svetloyar in Russia, we all like to wonder what may have happened to these great metropolises.

Just recently, divers exploring the shallow seafloor off the coast of the Greek island of Zakynthos thought they had come across a real-life version of a long-lost city when some very unusual underwater formations came into view, including some strange pillars, walkways and even what appeared to be courtyards. Writing in the journal Marine and Petroleum Geology, a team of environmental researchers have now revealed that these peculiar structures are not actually archaeological remains at all.

“The site was discovered by snorkelers and first thought to be an ancient city port, lost to the sea,” Julian Andrews, a professor of environmental geochemistry at the University of East Anglia, said in a statement. “There were what superficially looked like circular column bases, and paved floors. But mysteriously no other signs of life – such as pottery.”

^{Some of the pavement-like features seen at the site. University of Athens}

The serendipitously discovered site near Alikanas Bay resides just a few meters underwater; frankly, it’s easy to see why, upon first viewing, it could be interpreted as the remains of a city that had been crafted by ancient humans.

Had some unforetold disaster wiped out the unfortunate residents of a previously undiscovered and undocumented civilization? Had all the people living there escaped before the catastrophe hit, taking all their precious ceramic goods with them? Unfortunately for archaeologists, geochemical dating techniques revealed that these strange seabed features dated back to the beginning of the Pliocene era – about 5 million years ago – long before the genus to which humans belong to, Homo, walked the Earth.

After being carefully examined by archaeologists, geologists and professional divers from both Greece and the United Kingdom, it was clear that the disk and doughnut-shaped columnar features were a type of mineralization feature. They were being generated by the escape of chemicals, mainly methane, emerging from hydrocarbon-rich layers hiding below a semi-ruptured fault.

Microbes lurking in the sediment there appeared to be using the carbon in the methane as a source of energy. As they oxidized the methane, these bacteria and archaea were inadvertently changing the chemistry of the sediment they were living in to form a natural cement. To geologists, this is known as “concretion,” and it can result in a number of new rock formations.

^{This is, sadly, not some ancient column built by humans, aliens or very intelligent cephalopods. University of Athens}

“In this case the cement was an unusual mineral called dolomite which rarely forms in seawater, but can be quite common in microbe-rich sediments,” Andrews noted. “These concretions were then exhumed by erosion to be exposed on the seabed today.”

The researchers point out that concretion is quite rare in shallow waters, perhaps due to the greater concentration of methane jets and methanophilic microbes at greater depths. In fact, this type of methane seep is analogous to deep-sea hydrothermal vents, which are themselves home to a diverse range of extreme microbes able to thrive in their superheated, high-alkaline, methane and hydrogen-rich waters; the only major difference here is that this shallow methane seep is far, far colder.

This is a rather splendid discovery if you're geologically-inclined; however, if you were hoping to get the chance to do a bit of tomb raiding off the coast of Greece anytime soon, you're going to be disappointed.