Some say the sea connects us, others that it divides us. Of course, both are true. I live on the south coast of England, close to the English Channel, or, as the French call it, la Manche. France is less than one hundred miles away across the busiest shipping area in the world. Day and night, tankers and cruise ships ply across the water while fishing vessels and oil rigs mine its depths. Viewed from my apartment, the sea stretches out as still as a landscape painting, a paintbrush sweep of gunmetal blue blurring into the horizon and fading into white clouds.

But this view has not always been so watery. The Channel rests upon a lost world: below its surface lies an ancient forest floor, crisscrossed by pathways created by the feet of thousands of people traveling to and fro across a vast, nameless wilderness. Once, this stretch of terrain was part of continental Europe, a landscape of forests, plains, and rivers. And just a mile along the coast from my home, a hill called Hengistbury Head still holds that history fast in its stony cliffs.

Twelve thousand years ago there was no Channel, just a wooded landscape of broad valleys and intersecting rivers. But Hengistbury Head was a landmark even then. At 118 feet above sea level, it provided a vantage point for Stone Age hunter-gatherers following migrating herds of wild horses and cows, red deer, Arctic hares, reindeer, mammoths, wolves, and antelopes. On the flatter and more sheltered northern side of the hill, there was space for the camps of multilingual buyers and sellers, craftspeople, and travelers, all of whom had walked for hundreds of miles to reach this important business hub.

Human activity continued at Hengistbury for thousands of years more. But during this time, the icecaps were slowly melting. As it got warmer, the ground became increasingly swampy, the rivers wider, the lakes deeper, until, in 6200 BCE, disaster struck. The pressure of rising water levels in Norway triggered a series of landslides, which in turn caused an area of landlocked sea to burst its banks. The resulting tsunami rushed southward toward what was then a peninsula but would soon become a separate landmass. And when the waters finally leveled out again, the island I live on had been created—no longer joined to the landmass now called Europe.

In the centuries following the flood, Hengistbury became an important seaport and a significant burial site. Eleven unearthed Bronze Age barrows have been found to contain axes and cremation urns between 3,500 and 4,000 years old. The remains of a young woman were found inside one of them: she’d been cremated, then buried with an incense cup and amber, copper, and gold jewelry.

Then came the Iron Age, and fiercer times. By 700 BCE, Hengistbury had been strongly fortified with earthworks to protect the port and the industrial production going on around it. Imported lead, copper, silver, and gold were used to make a variety of goods including bronze coins, thousands of which have been found in the area. The worked metals were traded for imports of figs, glass, tools, wine, and pottery from the Mediterranean. Just as in the Stone Age, when hunter-gatherers plied their way back and forth across the wooded plains, it was an important international trading center.

Since the Roman conquest, Hengistbury has been less busy. In the nineteenth century it was heavily quarried for ironstone, which was stripped off the beach and dredged from offshore. As a result, almost half of the hill washed into the sea, and work is now underway to stabilize it. But even today it is possible to walk along the water’s edge and discover worked flints from the Stone Age, remains of Iron Age and Bronze Age firepits, and coins from different eras.

A few times a year, I battle the wind to climb up to the site of a Mesolithic encampment, close to where the Coastguard Station now watches over the sea. I sit on the low mounds of short tough grass and try to imagine how the Stone Age inhabitants made sense of it all. Over the years they watched familiar tracks, plains, and woodlands slowly being engulfed and listened to travellers’ tales of newly impassable rivers and important landmarks, now sunk and disappeared. On the Channel seabed, marine archaeologists have found Neolithic tools made from stone and flint, and the oldest piece of string ever found in the United Kingdom, in use millennia before the water came and cut us away from the continent.

The UK is about to experience another tsunami: Brexit. In 2016, the UK voted on whether to leave the European Union. The result, 51.9 percent “Leave” and 48.1 percent “Remain,” was only advisory and not legally binding, but because the government chose to implement it, as of this writing the UK will officially exit on March 29, 2019. Though self-inflicted, this separation will probably be almost as disastrous as the surge of water that cut us off from our continental cousins eight thousand years ago.

Today’s travelers come to Hengistbury Head not to hunt or trade but to watch heritage farm animals grazing peacefully, or to spot rare natterjack toads breeding in shallow ponds, or to thrill to the songs of larks rising in the evening air. And just like those Stone Age hunter-gatherers, these visitors still speak many languages. They include the Polish, Portuguese, and Romanian of local workers and the foreign tongues of tourists. Will Brexit finally silence them? We will soon find out the next chapter in our history. Perhaps it is not really the sea that divides us from each other, but ourselves.