Covered with fronds of billowing algae, the jumble of stone blocks and paving on the sea bed looked like the discovery of a century – a long lost Greek city hidden beneath the waves.
But rather than being the remains of an ancient Hellenic port, a set of ‘ruins’ discovered off the coast of Zakynthos in Greece, have a more mundane origin.
Archaeologists have revealed what appeared to be paved courtyards and classical colonnades are actually part of a natural geological feature that formed up to five million years ago.
The researchers say the mysterious structures – which at first glance appear to be man- made – were formed as methane gas leaked out from beneath the sea bed.
It will no doubt disappoint many who had hoped the discovery may be an archaeological time capsule to rival the lost Egyptian city of Heracleion, which was submerged 1,200 years ago.
The site was discovered by snorkelers just outside Zakynthos’s Alikanas Bay in 2013, between the island and the west Peloponnese peninsula of mainland Greece.
Huge circular columns were found to be sitting on top of the sea bed while around them patches of rectangular stones that looked like paving.
Nearby large doughnut shaped disks jutted conspicuously from the sandy sea floor.
The find sparked great excitement among experts who hoped it may be an ancient city that had been suddenly engulfed by tidal waves.
But underwater archaeologists who visited the site could find no sign of pottery or other evidence of human habitation.
Professor Julian Andrews, a geochemist at the University of East Anglia who led an analysis of the site, said it was understandable why the site was mistaken for a lost city.
The underwater ‘ruins’ were found in 2013 just off the coast of Alikana bay on the Greek island of Zakynthos (shown on the map pictured)
Rows of stone columns (pictured) were found in a straight line on the sea bed, lending support to the idea they had been part of an ancient city. But new research found they actually follow the line of an ancient fault line
Among the distinctive features discovered under the waves were large paving stone-like slabs (pictured) which appeared to form some sort of ancient courtyard
His team conducted detailed analysis of the underwater structures in an attempt to solve the mystery.
Professor Andrews said: ‘The site was discovered by snorkelers 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 researchers analysed the chemical composition of the structures (a doughnut shaped structure pictured) and found they were formed from a natural cement called dolomite
It appears these were formed by bacteria metabolising gas leaking out of the fault millions of years ago, which turned the sediment into dolomite. The columns (pictured) were caused by the gas bubbling through the sediment and building up over time
Chemical analysis and samples looked at under a microscope revealed the stone was formed of euhedral dolomite crystals and pyrite framboids, the researchers said
‘We investigated the site, which is between two and five meters under water, and found that it is actually a natural geologically occurring phenomenon.
‘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.’
The research team, which included scientists at the University of Athens and the Ephorate of Underwater Antiquities of Greece, have revealed their findings in the journal Marine and Petroleum Geology.
They used mineralogical and chemical tests to examine the underwater structures before conducing microscopy and x-ray analysis of samples.
Archaeologists who examined the site (pictured) were unable to find any pottery or other signs of human activity
They found the ‘columns’ and ‘paving stones’ were actually the result of an underwater gas leak from a fault just beneath the sea bed.
The escaping methane gas provided energy to microbes living in the sediment on the sea floor, which in turn turned the sediment into a natural cement known as dolomite.
This process, known as concretion, is common in microbe rich sediments, but as the fault had not fully ruptured, it formed tubes and columns in the sediment.
Some of the structures formed large doughnut shapes which over time have become covered in algae and sea creatures, making it harder to work out their true nature
Professor Andrews said the doughnut shaped structures appeared to form along a straight line, which is why they looked columns, had actually formed along the line of the fault.
In other areas the gas had bubbled along the sea bed, leading to slab like structures and elsewhere had created pipe-like formations.
Professor Andrews said: ‘This kind of phenomenon is quite rare in shallow waters. Most similar discoveries tend to be many hundreds and often thousands of meters deep underwater.
The researchers say it is rare for this sort of natural geological formation to occur in such shallow water, but have ruled out that they were created by human hands
With some of the stone structures appearing to form perfect rings (pictured) and columns, it is easy to see why they could have been mistaken for being manmade, but researchers insist they are entirely natural
‘These features are proof of natural methane seeping out of rock from hydrocarbon reservoirs.
‘The same thing happens in the North Sea, and it is also similar to the effects of fracking, when humans essentially speed up or enhance the phenomena.
‘Microbes in the sediment use the carbon in methane as fuel.
‘Microbe-driven oxidation of the methane then changes the chemistry of the sediment forming a kind of natural cement, known to geologists as concretion.
‘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.
‘These concretions were then exhumed by erosion to be exposed on the seabed today.’
THE LOST TREASURES OF EGYPT’S ATLANTIS
They have become known as the Atlantis of Egypt after laying submerged beneath the waves for more than a thousand years.
The cities of Heracleion and Canopus were built on the shifting ground of the Nile delta but were buried beneath 10 ft of silt as the sea engulfed them.
But in recent years archaeologists have raised enormous statues, golden jewellery and hieroglyphic tablets from the sea bed, revealing the splendor of these lost settlements.
Divers have spent almost two decades since painstakingly dredging them out of the deep.
Highlights include a 6ft (1.9 metre) heirogylphic tablet inscribed with a royal declaration from Pharaoh Nectanebo I and a 5.4m statue of Hapy, an Egyptian god who personifies the Nile’s floods.
Ancient texts record the existence of the settlements, which were the gateway to Egypt before Alexandria rose to prominence.
But the two trading hubs were lost – literally – to the sands of time until a chance discovery in 1996.
The artefacts raised from beneath the waves have now gone on display in a recent exhibition at the British Museum in London.