for National Geographic News
Changing sea levels and shifting sands helped Alexander the Great conquer the ancient island city of Tyre in one of his most famous military victories, new research shows.
In 332 B.C. the Greek military commander invaded the island just off the coast of modern-day Lebanon, then part of ancient Phoenicia.
New geological findings and computer models show that the growth of agriculture on the island caused sediment runoff, which spurred the formation of a long, thin submerged sandbar between Tyre and the mainland.
Alexander and his men cunningly exploited this sandbar, the findings suggest, to build a 0.6-mile (1-kilometer) raised path, or causeway, out of wood and stone.
Alexander's army marched from Macedonia to Egypt around 2,350 years ago, conquering every major city in turn.
But capturing the naturally protected Tyre posed a huge military problem. (See a photo of the ruins of Tyre.)
"Building a bridge out to sea was a real challenge at this time," said Nick Marriner of the University of Aix-Marseille in France, lead author of the study.
Marriner's team reports its findings in the current online issue of the Proceedings of the Academy of Sciences.
No Cranes or Concrete
To understand how Alexander constructed his causeway, Marriner and his colleagues drilled out four cores from the sediment around the present-day peninsula of Tyre, now called Soûr. (See map of Lebanon.)
By studying the layering of soils inside the cores, the scientists were able to piece together the last 10,000 years of coastal activity in the region.
The researchers used a computer model to process their soil data and reconstruct tidal and current patterns.
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