Low tides reveal Bronze Age fortress that likely defended against Irish mainland

Low tides on Ireland's western coast have revealed the remains of defensive walls that are likely Bronze Age ramparts.

Archaeologist Michael Gibbons discovered the ramparts, which are made of large limestone blocks, on a partially submerged isthmus, a narrow strip of land between two parts of the sea. But he's only recently obtained photographs of the site, which has enabled him to publicize the ramparts for the first time.

The isthmus, located in County Mayo's Clew Bay between Collanmore Island and the mainland near the village of Roscahill, is usually flooded by seawater, Gibbons told Live Science. However, a road across it can be used at very low tides.

The ramparts are about halfway across the roughly 1-mile-long (1.6 kilometer) isthmus; the remains of a wall nearest the mainland are about 590 feet (180 meters) long, while the remains of a larger wall nearest the island are about 820 feet (250 m) long, he said.

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Both ramparts cut across the isthmus and seem to have served to protect the isthmus and island from attacks from the mainland.

"They are providing a defensive wall, at a time when sea levels were considerably lower than they are now," Gibbons said.