Home / Technology / Ancient Humans Built the Earliest Known Defense Against Sea Level Rise 7,000 Years Ago

Ancient Humans Built the Earliest Known Defense Against Sea Level Rise 7,000 Years Ago

Approximately 7,000 years ago, a group of ancient humans built the first-known seawall in an attempt to keep rising tides from inundating their village. It’s the earliest known structure of its type and it shows how Neolithic communities attempted to adjust to the massive sea-level rise kicked off by the ending of the last Ice Age.

The wall is located at Tel Hreiz, a settlement in what is now Israel that existed some 7000 – 7500 BP (Before Present). A number of Neolithic settlements have been found submerged off the coasts of various countries — the earliest human settlements were often near both oceans and rivers, and older settlements are found farther off-shore than later ones, illustrating how sea-level rise at the end of the last ice age impacted human settlements. When constructed, the now-submerged village sat nearly 10 feet above the water. This settlement would have been created during a time when sea levels were rising rapidly, with a mean annual change of 2.6mm per year.

Tel Hreiz was identified as an archaeological site in the 1960s but has never been systemically excavated. The area has instead been surveilled for features when storms and tides exposed previously hidden sections of the village, including the highly unusual sea wall, which was exposed by storms and surveyed in both 2012 and 2015. It runs for more than 100 meters with a dog-leg in one section. The northern limit of the wall has been found, but the southern remains under sand, and the wall’s full extent is unknown.

The image below shows where various artifacts have been found, and their relation to the wall itself.

Seawall-Site

Various objects located during the investigation and their locations relative to each other.

So, how do we know it was specifically built to hold back the ocean, rather than for some other purpose? There are multiple clues.

First, when the Pottery Neolithic village stood here, the sea wall sat between the sea and the village. Only one hearth has been found on the seaward side of the wall and the land between the wall and the sea, known as a swash zone (the turbulent area where waves wash up on the beach after breaking) wouldn’t be good for grazing, animal husbandry, or freshwater supply. The chance that the structure was intended to be a harbor or breakwater is remote; the earliest-known stone-built harbor dates to 4500 BP, thousands of years after this structure was built. Early harbors were built in areas with natural features like bays, which Tel Hraiz lacked (and still lacks today). Archaeological finds suggest the village persisted for 300-500 years, that it was initially built well away from the water, and that the rapid sea-level rise occurring all over the world as a result of glacier melt inundated many of these communities. Drowned prehistoric villages are fairly common all over the world, but none so old has ever had a feature like this.

It is not clear why the villagers thickened one section of the wall, but it was built with several different architectural styles. The authors note:

Despite these different building styles, the boulder-built feature is a continuous and unified architectural entity which forms a wall. This is evident in the arrangement, nature and size of the stones; aside from the small dogleg, the boulders are aligned in a consistent and uniform direction and make up a relatively straight and continuous line parallel to the coast. They also follow the same bathymetric depth contour; representing the past topographic contour of the prehistoric coastline. Notably, for its entire length, it is free-standing and with the exception of the apparent stone wall fragments associated with the dogleg and the hearth (see below), the wall is not attached to any domestic structure in the village.

The boulders they used didn’t just come from farther up the shore — the nearest source of these stones would have been the riverbed and river mouth of what we now call the Oren and Galim Rivers, 2.28 miles (3.8km) and 0.96 miles (1.6km) away, respectively. Individual stones have likely shifted and some may have washed away in storms, but the wall remains a contiguous and highly visible feature in the landscape — and very clearly artificially constructed.

Even a mile is a fair distance to walk with stones this large. The visible rocks of the wall are roughly 20-39 inches in diameter (50-100cm), about 39 inches (100cm) tall, and weighed 200-1000kg. For a small community in the Pottery Neolithic time period, this wall was a huge investment in resources, and it may have been extended one or more times to provide additional protection. There is a second known example of an ancient seawall in the area, though it’s still much younger — there’s a boulder-built seawall dating to 3100-3500 BP in Atlit North Bay, some 1.8 miles south of Tel Hreiz.

This image shows the shift in Modern Sea Level (MSL) between today and the PN (Pottery Neolithic) period. PNSL refers to the sea level during the Pottery Neolithic period, approximately 7000 – 7500 BP (Before Present).

In the end, all the pieces of the puzzle point towards the same conclusion. A group of humans founded a village during a time when the town sat high and dry. Decades or centuries later, they realized that the changing climate threatened their way of life and they fought to keep their homes. Every single boulder in that 100+ meter wall represents a 200-1000kg rock moved over distances of at least a mile at a time when every calorie was dearly purchased. They might have had cows. They didn’t have wheels. They did it anyway.

We know that Neolithic people deployed a variety of sophisticated strategies to manage water in various ways (the article goes into more detail on this), but the seawall found here is unique for its age. The world of that era was astonishingly empty by our standards. They could’ve gone somewhere else, right?

Maybe. But they didn’t. There’s something deeply human in that. The meters of sea-level rise they were forced to contend with would challenge the flood-managing capacity of a modern first-world nation, even in a best-case scenario. What did they have? Rocks. Imagine looking at the rising ocean when the first, last, and pretty much only tool you’ve invented for holding it back is sticking two stones next to each other and filling gaps with sand and clay.

“If they’d known what they were up against, they never would have tried,” some might say, ignoring the history of every doomed cause, last stand, and hopeless fight on Earth. Truth is, they might have tried anyway. There’s something deeply human in that, too. It’s what connects the nameless Neolithic residents of what we now call Tel Hreiz with people across the Pacific on low-lying islands, or in the Arctic, where melting permafrost is driving significant land losses and temperatures have warmed faster than anywhere else on Earth. The amount of ice melting off Greenland each year is accelerating and the island now loses 7x more ice per year than it did in the 1990s. Luckily, the rate of sea-level rise happening now is much lower than when the great ice sheets were melting off the planet, but the number of people at risk today is larger than the total number of humans alive on planet Earth in the Neolithic era.

We, of course, have far more than rocks at our disposal. But we also have far more to lose and fewer places to go.

Updated (5/12/2020): This is one of my favorite stories that I’ve ever written, though I’m not just resurfacing it for that reason. A number of readers raised additional questions of interpretation in the comments — namely, why do we think this is a wall built against sea-level rise, rather than for other purposes? There are answers to these questions, and I’d like to address them.

Humans build walls for specific purposes. To understand what those purposes are, archaeologists examine a number of site characteristics, including the layout and structure of the wall, its location relative to the town or village it guards, and what other people in the area were building at the same time. This wall would not have been built for agriculture — it’s far too close to the historical shoreline, and the area was periodically inundated even before the sea began to rise. The ground would not have been good for grazing or beast-penning for the same reasons (we don’t actually know if these people had domesticated cattle yet, so it’s not even clear they’d be building these kinds of pens yet in the first place).

The wall wasn’t a defensive structure (it would have curled around the buildings to defend from land as well if it had been). It wasn’t an agricultural terracing system — there’s no evidence of other terraces, and you wouldn’t build a large, complicated terrace directly over the rapidly-rising ocean.

Could they have been fish traps? This was an interesting question, but the evidence suggests no. The Stilbaai Tidal Fish Traps are known examples of ancient fish traps found on the coast of West Africa. One major characteristic of these structures is that they are enclosed, made of tightly packed stones, and do not resemble the overall structure above. If the thickest part of the wall above had been hollow in the center (and larger), it might have functioned in this manner, but neither is the case.

It may help to know that we have found a great many drowned littoral villages of this sort all over the world. We have known for centuries that rivers and oceans helped nourish (literally and figuratively) early human civilizations. Drowned villages in areas corresponding to lower sea levels during the last ice age are common. There are signs in other villages nearby of various other measures humans took to combat climate change, including digging fresh wells and attempting to raise the water table to avoid brackish contamination from rising water.

We know, factually, that humans once dwelled in areas that we are now cut off from due to sea-level rise. We know that humans generally fight to remain in their homes, then and now. The surprise of discovering that humans built a seawall to fend off climate change is surprising for how early they built it, not for the fact that they tried.

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