Several years ago, divers off the Greek island of Zakynthos came across what looked like ancient columns and column bases, perhaps the remains of an long-lost civilization now underwater. Authorities were sent in to investigate, and what they found might disappoint archaeologists.

The underwater "lost city" was not made by an ancient civilization, but by microbes millions of years ago, according to a study published today in the journal Marine and Petroleum Geology. Archaeologists couldn't find any remains — like pottery and other objects — that indicated people had lived at the site, The New York Times reports.

The pipe-like and doughnut-shaped objects that looked like ancient columns were found to be the result of a natural phenomenon. The area was a cold seep: a spot on the sea floor where methane emanated into the water. The sediments in the seabed contained microbes, which consumed methane for energy and eventually changed the chemical composition of the sediments to create concretions of a rock called dolomite.

The microbes responsible for the structures possibly operated about 5.3 to 2.6 million years ago, during the Pliocene age, according to the study. The "columns" reappeared over time as the seabed eroded.

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