Ever heard of the city of Helike? For a long time it was as lost (and considered as mythical) as the city of Atlantis. Then one day someone found a coin from Helike, and the search was on. Take a look at how people found the ancient city of Atlantis — on land.
Atlantis was a legend — a city that sank into the sea after a "day and night of misfortune." Helike might very well be the city upon which the Atlantis legend was based. For quite some time, scholars of Greek history found references to the city of Helike. It was mentioned in The Iliad as having sent a ship out to fight in the Trojan War. It joined up with twelve other cities and maintained an ordered stretch of land. It was a naval power. And it sank into the sea. No trace of it was left.
Over time, people became certain that it was no more than a twisted off-shoot of the Atlantis legend. A city might be razed or depopulated by some natural disaster, but wiped off the Earth without a trace? How was that possible? There was no sign of the city at all. And then, about a hundred years ago, a coin turned up. It was a small, unremarkable coin that had a face in profile. And it had the name of Helike on the other side. It let people know that they were chasing more than a just a legend.
Searches began in earnest, then. They gradually intensified over the years, culminating in The Helike Project in 1988. The project first used sonar to sound out the ocean. There was nothing. They took the search to the land, still finding nothing. At last, they thought that the legend might be a half-truth. What if Helike hadn't sunk into the sea, but a kind of sea bubbled up to claim Helike? The project began searching for signs of dried-up lagoons inland, and in 2001, found ancient Greek ruins buried deep in the Earth. When they looked at the coins they found, they realized what had finally happened to Helike.
Helike was built on a liquefaction zone. When an earthquake hits such a zone, the soil suddenly behaves as though it were water. Suddenly, all the buildings sink like they were dropped on the sea. Meanwhile, the sea — and any surrounding groundwater, is rushing upwards to meet them. In 373 BC, an earthquake turned the ground beneath Helike into liquid, and the entire city sank into a newly-made lagoon. Meanwhile, parts of the coast in the area broke off and slid into the sea, causing a massive tidal wave that rushed across the sea, rebounded off the far coast, came back, and buried the sunken city under water. A day and night of misfortune, and Helike was gone. Over time, silt and dirt washed into the lagoon and it dried up, burying the city in dirt. The lost Atlantis isn't lurking under the sea. It's buried in the ground.