The recent discovery of two long-lost cities off the coast of Egypt has been hailed as one of the most exciting finds in the history of marine archaeology.
But the location of the sunken cities of Menouthis and Herakleion might have remained a mystery if not for a unique collaboration among scientists, archaeologists and underwater explorers.
``These ancient cities disappeared more than 1,500 years ago,`` says geophysicist Amos Nur, the Wayne Loel Professor of Earth Sciences.
``Offshore geophysical surveys led to their discovery, and earthquakes may have been responsible for their demise,`` he adds.
Nur will moderate a special session about the Menouthis/Herakleion discoveries on Monday, Dec. 18, at 8:30 a.m. at the fall meeting of the American Geophysical Union in San Francisco.
Among the researchers scheduled to attend the half-day session is Franck Goddio, the French marine archaeologist who last June announced the discovery of the submerged cities in the Bay of Aboukir about 15 miles (25 kilometers) east of Alexandria, Egypt.
Goddio and his divers made headlines when they unearthed from the bottom of the Mediterranean Sea giant marble statues and fractured columns - some dating back to the time of the pharaohs.
``In the ancient world, a major center of various religions and cults existed here,`` says Goddio, director of the European Institute of Submarine Archaeology in Paris.
``Numerous sources of ancient literature verify the existence of the once famous region,`` he adds, noting that some authors described Herakleion and its sister city, Menouthis, as opulent and decadent.
``These cities were not only renowned for their riches and lifestyle, but also for their many temples dedicated to the gods Serapis, Isis and Anubis,`` says Goddio.
``Among others, the Greek historian Herodotus described a temple of Hercules in Herakleion, which he visited during the journey through Egypt he began in 450 B.C.,`` he adds.
The search for the missing cities began in 1996 - a challenging task, recalls Goddio, because it required surveying a 100-square-mile area of the Mediterranean.
``We recognized that the work would be only successfully achieved if a team gathered from diverse disciplines could be formed,`` Goddio says, so he and the Egyptian Supreme Council for Antiquities assembled specialists in geophysics, archaeology, history and marine diving to find evidence of the vanished metropolises.
To map the sea floor, geophysicists used a catamaran specially equipped with echosounders, side-scan sonar and nuclear magnetic resonance (NMR) magnetometers towed in parallel.
``The scientists only had one day left aboard the ship when they finally discovered Herakleion submerged in silt less than 24 feet [8 meters] below the sea surface,`` according to Nur.
What caused these great cities to collapse and sink?
A likely answer is earthquakes.
``In Alexandria itself,`` writes Nur, ``both historical records and archaeological evidence of collapse have shown that the city was devastated both onshore and offshore by an earthquake in the mid- to late-eighth century A.D., and by one or two earlier earthquakes sometime during the period 200 to 600 A.D.``
He points to rows of columns that all fell in the same direction - strong evidence that a devastating earthquake struck the Alexandria region.
The sinking of the cities is more difficult to explain, Nur concedes, but he says land may have subsided as a result of earthquake-induced liquefaction of the sea floor, or by tsunamis - giant walls of water that sometimes sweep across the shoreline in the aftermath of a marine earthquake.
The Smithsonian Institution`s Daniel J. Stanley, a specialist on the geology of the Nile River Delta, also will address the Dec. 18 AGU session. He points out that Herakleion - originally a shipping port at the mouth of the Nile - may have been destroyed and flooded after a branch of the river abruptly shifted course during the first millennium.
Italian historian Emanuela Guideboni will provide evidence from Arabic, Latin and Byzantine sources documenting 14 centuries of earthquakes in the Alexandria region from 320 to 1303 B.C.
However, Jean Yoyette of the College de France in Paris will argue against the earthquake theory, noting that some ancient texts say nothing about major tectonic activity having occurred in the region 1,500 years ago.
``Because the historical and archaeological information in this region is so sparse and incomplete,`` says Nur, ``it is not possible as yet to identify the earthquake faults that devastated Alexandria and Aboukir.``
However, he will discuss three likely locations of the fault system when he addresses the AGU.
``The case of Alexandria and Aboukir highlight the emerging importance of archaeological information in general in helping to predict earthquakes,`` Nur adds, noting that other densely populated coastal regions around the world face similar earthquake hazards today.
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