Dune du Pilat: the Millennia Old « Pile of Sand »
by Chloe Destremau
The sand, soft and malleable, sank into my feet with each step taken. I found footprints, belonging to the few that now stood at the top of the Dune, and I used their crevice as a step. My leg muscles flexed, stretched, and worked, but my heart did not falter, and I did not stop. As I climbed, two worlds revealed themselves: to the east, one of a tired forest, rows of evergreens and scorched openings scattered across, and to the west, a cerulean ocean, stretching far beyond the horizon, with a stroke of sand in the middle. The sand stood as a barrier between the two, only 616 meters in width. It is a canvas only found here, in the oyster farming commune called Arcachon, nestled between the Landes forest and the Bay of Biscay.
My efforts came to an end, at last, when I had no more sand to climb. And there, at the top, I stood at 100 meters above sea level, on the tallest Dune of Europe, the Dune du Pilat. Pilat, from Gascon dialect, simply stands for mound, or pile. I was standing, literally, on a pile of sand. Hills of white rolled parallel to the forest and the water. It seemed infinite. But I knew it was not, that it did end eventually, so I started again, walking the crest.
Below me, a group of kids launched themselves down the eastern side, « côté Terre », a hundred meters of steep, straight sand. They barrelled downward in bursts, half-running, half-falling, their feet sinking with each stride until they reached the foot of the pines. Their laughter echoed back up the cliff, straight into my ears.
Beyond stretched the Forest de La Teste-de-Buch, where maritime pine and pedunculate oak dominate the sporadic canopy. From the 17th century on, gemmers tapped the pines for resin, making solvents, paints, glue, waxes, and medicines. Once the trees had died, their collected tar and burnt wood were used for caulk, waterproofing, and medicine, among much else. But the forest has rested since the discovery of synthetic substitutes in the 1970s, rendering pine resin obsolete. The remnants of the forest’s history are only visible in the old huts, cellars, and sheep pens of the resin workers still present. Wildfire burnt much of the forest in 2022, but young growth has sprouted since, creating a mosaic of emerald greens and ash.
The kids I was watching looked around for a path and found none. I was unsure where they would go then. The campsite in the middle of the burnt forest was deserted, and the climb back up the Dune seemed impossible. But they were kids, and anything was possible at that age. They got on all fours and tackled the mound, while I continued my hike.
The Dune du Pilat stretches for only 3 kilometres, but few make the march. By the second hill, I was walking on my own. I wondered if I would cross paths with a barred grass snake or a western green lizard, but the day was hot, and only a pair of gulls paid me a visit as they flew overhead.
I stopped at the fourth hill for a pause and a look. The view of the west, « côté mer », stared back at me with its mesmerising waves, inviting me to come down for a swim. I could easily see Cap Ferret, the headland protecting the basin from the Atlantic, its lighthouse a visible monolith standing among the greenery. In the middle of the water lay the Banc d’Arguin, the shifting sandbank at the mouth of Arcachon Bay, where tides and currents clash. Several boats were anchored, and a couple of lucky swimmers were enjoying the turquoise waters. I took a sip of water and let the warm sand sift through my fingers. This soft white sand once belonged to that very sandbar, before the wind carried it inland, grain by grain, to form the ancient mound beneath me.
The Dune du Pilat is four thousand years old. Here at the very top, I sit on its youngest layer, only two hundred years old. The Dune is not static; much like the sandbar, it moves and shifts with the climate. It has, in its millennia-old existence, buried marshes, forests, and villages as it traveled inland. On its western slope, four paleosols—distinct soil layers—trace the stages of its formation through time.
Here at the summit, if I were to dig, I would uncover old gemmage pots and the remains of maritime pines, planted in the 19th century under Napoleon III’s decree. That decree followed when rumours spread that the Dune was growing so tall it might one day engulf Bordeaux, some fifty kilometres away. To counter the threat of its advance, the French engineer Nicolas Brémontier put into practice Charlevoix de Villiers’ idea: using pine forests to anchor the sand and halt its movement. Beneath my feet lies the result of that effort—the fourth paleosol, a mix of sand and forest debris, formed between the 1500s and 1800s, once known as the Dune de Grave. Yet despite the scale of the undertaking, by 1887 the sand had already proven too powerful:
To the east of the Banc d’Arguin, we are currently witnessing the formation of a new dune which is engulfing forests of 15m high pine trees under the sand. – M. Clavel (1887) about the formation of the Dune du Pilat.
My descent down the Dune becomes a journey through time when I reach the third paleosol, an undulating layer of old parabolic dunes strewn with shells, cockles, and scallops. Archaeologists have uncovered flint tools, pipes, coins, and ceramics here, dating back to the 16th century. In those days, there was no towering dune; the climate was gentle and humid, allowing forests to claim the sandy ground and humans to settle along the coast.
The sand is softer here than at the top, and soon my shoes fill with it, the grains finding every nook and crevice of my feet until they feel like stumps. I stop to empty them, only for the sand to crawl back in with each step. Eventually, I give up, take them off, and continue barefoot.
The second paleosol lies below, a layer of sand deposited during a dry prehistoric period between 2000 and 500 BCE. It contains fossilised vegetation and traces of human presence from the first Iron Age, including evidence of a salt farm. At that time, the dunes rose only four to five meters above sea level. At their base stretched a shallow water basin, marked today by hardened plates of diatom skeletons—microscopic phytoplankton that once thrived there.
At the shoreline, where waves lap at the sand and leave strands of algae and zostera seagrass at my feet, I come across the first paleosol. The oldest layer lies just above the waterline, marked by fossilised pinecones and tree stumps—some 4,000 years old—resting on a hardpan darkened by sand and iron oxide. Among them, the remains of birch, hazel, Scots pine, and oak tell of a cold, humid climate that once prevailed between 8000 and 2000 BCE.
But the water is warm today, the sun blazing overhead warming my skin, and I ponder going for a swim.
The Dune du Pilat only became a big « pile of sand » in the last centuries and continues to grow every year. Regional and communal agencies now monitor its evolution, noting a gradual loss in height but a steady advance inland. At the crest, the sand is pushed eastward, eating away at the forest, creeping towards roads and villages one sand grain at a time. Perhaps in a few centuries, it will reach Bordeaux after all, in a gargantuan, millennia-old pile of sand.
Note about the writer (photo right): Chloe Destremau is a freelance writer and the daughter of Christy Destremau, founder and owner of France Off the Beaten Path Tours.
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