Divers Intrigued by Huge Underwater Structure

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 attributed to the end of the last ice age, causing huge ice sheets to melt, and forcing humans to resettle away from the coast.

The wall measures an average of 65 feet wide and just 6.5 feet high, and is covered by 30 feet of water. Giant granite standing stones dot the wall at regular intervals, protruding above it along two parallel lines, according to the BBC.

Scientists suggest the standing stones may have once held a net of sticks and branches to catch fish.

“It was built by a very structured society of hunter-gatherers, of a kind that became sedentary when resources permitted,” archaeologist Yvan Pailler, coauthor of a paper about the finding published in the International Journal of Nautical Archaeology this week, told the BBC. “That or it was made by one of the Neolithic populations that arrived here around 5,000 BC.”

The wall was first discovered in 2022 and extensively mapped later that year.

In August, the discovery of a separate Stone Age settlement off the coast of northern Denmark made headlines. The excavated settlement was similarly flooded by rising sea levels after the last ice age and “was positioned directly at the coastline,” as underwater archaeologist Peter Moe Astrup told the Associated Press at the time. “What we actually try to find out here is how was life at a coastal settlement.”

According to the archaeologist, sea levels rose by around 6.5 feet per century approximately 8,500 years ago.

“It’s like a time capsule,” Moe Astrup said. “When sea level rose, everything was preserved in an oxygen-free environment… time just stops.”

As we continue to explore how our ancestors lived following the last major climate event, it’s just as much of a relevant a topic today. The United Nations warns that hundreds of millions of people around the world who live along the coast are being threatened by climate change-induced coastal erosion and flooding, which could one day force them to relocate inland — just like the early settlers may have once done thousands of years ago.

More on the ice age: Ice Age Humans Were Skilled Firebenders, Scientists Find