Look at a map of the southwestern Netherlands and Walcheren stands out: a tidy diamond shape tucked between the Eastern Scheldt to the north and the Western Scheldt to the south, the two arms of the river that eventually reaches Antwerp. The two sides facing the open North Sea are dunes, soft and shifting; the rest is dyke, hard and engineered. In the middle sits Middelburg, the provincial capital, with the harbour town of Vlissingen nine kilometres south and the smaller town of Veere to the northeast. Once an island in fact, Walcheren is now an island only in memory. The Sloedam railway embankment of 1871 tied it to Zuid-Beveland; postwar polders thickened the connection; the Veerse Gatdam, completed in 1961, knitted it to Noord-Beveland. You can drive on and off without ever feeling you have crossed water.

The Romans called the place Wallacra and used it as a jumping-off point for crossings to Britain. They left behind a temple to Nehalennia, a local goddess whose altars sailors stacked with thanks for surviving the North Sea — which in those days was even less forgiving than it is now. The Vikings followed. In the ninth century the Dane Harald, brother of Rorik, made Walcheren the seat of his power in the Low Countries. Centuries later, in 1588, the island helped doom the Spanish Armada in a quieter way: Dutch rebels and English fighters who held Walcheren blocked the Duke of Parma's deep-water port at Antwerp from the sea. With no friendly harbour to retreat to, the Armada faced dwindling supplies, and Admiral Medina-Sidonia fled north. The flat little diamond at the river's mouth had once again decided who controlled the Channel.

In July 1809, 39,000 British soldiers stepped ashore on the island. Their commanders wanted to draw French troops away from Austria and seize the French fleet at Vlissingen. They did capture Vlissingen, but the Austrians had already lost at Wagram and were suing for peace, the French ships had slipped upriver to Antwerp, and the marshes began to do what marshes do. Mosquitoes carried something the British called Walcheren Fever, almost certainly a combination of malaria and typhus. More than four thousand soldiers died of disease. One hundred and six died in combat. By December, what was left of the expedition limped home. The episode entered British military memory as a model of what happens when an army underestimates a wetland.

The 1944 inundation was not an accident. By autumn, the Allies needed the port of Antwerp to keep their advance across northwest Europe supplied. They had taken the city itself, but its sea approach ran past Walcheren, and the Germans had fortified the island into Festung Walcheren, bristling with coastal batteries. So the RAF struck the dykes. The sea came through the gap at Westkapelle, then through Vlissingen, then through Veere — a controlled drowning that pinned defenders to the high ground and let amphibious assault craft come in. On 1 November, British Commandos landed at Westkapelle as part of Operation Infatuate. The Canadian Black Watch and Calgary Highlanders fought their way along the narrow Walcheren Causeway, the Highlanders losing 64 killed and wounded in a few brutal nights. By 8 November the island had fallen. The water did not leave until October 1945. Farms were lost, orchards were killed by salt, and entire villages had to be rebuilt. Walcheren remains the most extreme case in modern history of a coast deliberately flooded as an act of war.

Today, the dykes hold and the dunes are planted with marram grass against the wind, and the rebuilt towns wear their history lightly. Middelburg's lace-windowed houses and stepped gables hint at the wealth that came through Vlissingen when the Dutch East India Company anchored its ships here. Veere keeps the old harbour wall where Scottish wool traders once tied up. Westkapelle has rebuilt its lighthouse and its sea wall; the breaches the RAF opened are long since stitched shut. From the air, the diamond reads cleanly: dark green polders, pale dune ribbon, the silver line where dyke meets sea. Walcheren has agreed, again, to be land.