The vast majority of our planet’s oceans remain entirely unexplored, meaning they’re full of tantalizing treasures hidden from sight.

In a particularly cool example, French marine archaeologists discovered an enormous undersea wall that measures almost 400 feet in length, as the BBC reports — the biggest underwater construction ever found in France.

The wall was discovered off the coast of Brittany. Scientists believe the wall dates back to the Stone Age, roughly 5,000 BC, and may have been part of a fish-trap or a dyke to protect against rising sea levels — a striking parallel to the threats of global warming we face today.

However, while human activities have become the largest contributor to global warming in the 21st century, rising sea levels during the early Holocene are largely a

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