Atalanti (the modern Talandonísi), is a small island off Locris

Locris

Locris was a region of ancient Greece, the homeland of the Locrians, made up of three distinct districts.-Locrian tribe:...

, in the Opuntian Gulf, said to have been torn asunder from the mainland by an earthquake

Earthquake

An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...

. In the first year of the Peloponnesian War

Peloponnesian War

The Peloponnesian War, 431 to 404 BC, was an ancient Greek war fought by Athens and its empire against the Peloponnesian League led by Sparta. Historians have traditionally divided the war into three phases...

 this previously uninhabited island was fortified by the Athenians

Athens

Athens , is the capital and largest city of Greece. Athens dominates the Attica region and is one of the world's oldest cities, as its recorded history spans around 3,400 years. Classical Athens was a powerful city-state...

 to prevent Locrian

Locrians

The Locrians were an ancient Greek tribe in Greece. The Locrians spoke the Locrian dialect, a Doric-Northwest dialect, which indicates that they may have been relatives of the Dorians. They inhabited the ancient region of Locris in Central Greece....

 pirates attacking Euboea

Euboea

Euboea is the second largest Greek island in area and population, after Crete. The narrow Euripus Strait separates it from Boeotia in mainland Greece. In general outline it is a long and narrow, seahorse-shaped island; it is about long, and varies in breadth from to...

.. In the sixth year of the war a part of the Athenian works was destroyed by the sea, with half the ships on the beach destroyed. Thucydides

Thucydides

Thucydides was a Greek historian and author from Alimos. His History of the Peloponnesian War recounts the 5th century BC war between Sparta and Athens to the year 411 BC...

 reports that following an earthquake, the sea receded from the shore before returning in a huge wave. Citing similar events at Peparethus and Orobiae, he suggests that earthquakes and such "sea events" are linked - we now know that such tsunami

Tsunami

A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake...

 are in fact caused by earthquakes. In 421 BC

421 BC

Year 421 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Consulship of Vibulanus and Barbatus...

, the Peace of Nicias

Peace of Nicias

The Peace of Nicias was a peace treaty signed between the Greek city-states of Athens and Sparta in the March of 421 BC, ending the first half of the Peloponnesian War....

returned Atalanta to Sparta.