Tsunami That Razed Rome Studied Anew

March 10, 2008 -- "The sea was driven back, and its waters flowed away to such an extent that the deep sea bed was laid bare and many kinds of sea creatures could be seen," wrote Roman historian Ammianus Marcellus, awed at a tsunami that struck the then-thriving port of Alexandria in 365 AD.

"Huge masses of water flowed back when least expected, and now overwhelmed and killed many thousands of people... Some great ships were hurled by the fury of the waves onto the rooftops, and others were thrown up to two miles from the shore."

Ancient documents show the great waves of July 21, 365 A.D. claimed lives from Greece, Sicily and Alexandria in Egypt to modern-day Dubrovnik in the Adriatic.

Swamped by sea water, rich Nile delta farmland was abandoned and hilltop towns became ghost-like, inhabited only by hermits.

The tsunami was generated by a massive quake that occurred under the western tip of the Greek island of Crete, experts believe.

Until now, the main thinking has been that this quake -- as in the Indian Ocean tsunami of Dec. 26, 2004 -- occurred in a so-called subduction zone.

A subduction zone is where two of the Earth's plates meet. One plate rides over another plate which is gliding downward at an angle into the planet's mantle.

Subduction zones usually have measurable creep, of say a few inches a year. But as the rock becomes brittle and deformed at greater depths, these zones can also deliver titanic quakes, displacing so much land that, when the slippage occurs on the ocean floor, a killer wave is generated.

The 365 A.D. quake occurred at a point on the 300-mile-long Hellenic subduction zone, which snakes along the Mediterranean floor in a semi-circle from southwestern Turkey to western Greece.

Researchers in Britain have taken a fresh look at this event and have come up with some worrying news.