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Geoarchaeology

The Fall of Tyre Revisited

How did the ancient city of Tyre, naturally defended by the sea on all of its four sides, finally succumb to Alexander the Great? Scientists from the CEREGE,1 in Aix-en-Provence, have provided an answer which was revealed by new geoarchaeological research.2 “The invaders used a sandbank created by Mother Nature,” explains Christophe Morhange, who co-led the study with Nick Marriner. Based on diagnostic shoreface sediments and macro- and micro-fossils, the group has shown that Alexander's engineers exploited a shallow sandbank to build a ~ 1000 m-long causeway and breach the city's defences. But how did this natural bank form?

 

tyre

 

Unlike traditional archaeologists, who study man-made structures and objects, the team of geomorphologists have used Tyre's coastal sediments as historical archives. A series of 10-15 m cores drilled on the present isthmus were analyzed in the laboratory and unravelled an 8000-year-old story.

Computer models run by the team demonstrate that Tyre's unique geomorphological context–an offshore island in proximity to the coastline–dissipated swell and wave energy, conducive to the deposition of fine-grained sediments. The low-energy conditions are corroborated by the sedimentological and macro- and micro-fossil data from the isthmus cores. Radiocarbon dates, used to constrain this narrative, show that the growth of the proto-spit was particularly pronounced from the Bronze Age onwards, culminating in a sandbank 1 to 2 m below the water surface by the time of Alexander the Great.

“When the city eventually fell to the Macedonian armies, Alexander strengthened the bridge using rubble from destroyed parts of the city,” comments Marriner. In its most advanced stage, the causeway might have reached an average width of 200 Greek feet, or ~ 60 m. “ We still have to unearth physical remains of the bridge,” says Marriner, “but the sediments and fossils already confirm that Alexander's causeway led to a human-induced transformation of the Tyrian coastal system.” Material rapidly accumulated on either side of the artificial sea bridge, eventually linking Tyre to the adjacent coastline by a spit of sand, commonly referred to as a tombolo by geomorphologists.

“Our study shows that the tombolo is a relic of the events that unfolded in 332 BC,” adds Morhange, “an interesting example of how combined applied geological and geomorphological approaches may help answer archaeological questions.”

 

Jason Brown

Notes :

1. Centre européen de recherche et d'enseignement des géosciences de l'environnement (CNRS / Université Provence Aix-Marseille I).
2. N. Marriner et al., “Holocene morphogenesis of Alexander the Great's isthmus at Tyre in Lebanon.” Proc Natl Acad Sci U S A. 104(22): 9218-23. 2007.

Contacts :

Nick Marriner
CEREGE, Aix en Provence.
marriner@cerege.fr


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