When Saeftinghe Castle was built - probably between 1263 and 1293, despite the often-cited date of 1279 - it sat at the most lucrative chokepoint in the southern Netherlands. The Western Scheldt and the Eastern Scheldt were not yet fully connected. Around 1400 a series of floods welded them together, opening the route that would let Antwerp grow into the commercial capital of northern Europe. Saeftinghe controlled the split. From a square keep with two round towers and a residential wing, the lords of Flanders levied tolls on every ship that came up the Honte. In 1375 the account books mention a house for the toll collector, a small galley with a sail and four oarsmen, and a smaller boat - the apparatus needed to chase down anyone who tried to sneak past. The castle's buttresses leaned outward, which was bad defensive practice but excellent for keeping walls standing when the ground beneath them slumped in a flood.

Saeftinghe's problem was geography. By the mid-1300s, most of the dikes around the castle had failed, and the building stood on a gors - a high salt-marsh that the tide normally did not reach. The Flemish countess and later the Counts of Flanders kept patching a ring dike around the castle alone, then around its harbor 80 meters east of the walls. Between 1375 and 1539, records mention damage to that dike again and again. In 1382 the rebels of Ghent besieged the place. In 1452 the garrison marched out to fight Ghent and got beaten badly. In 1484 Maximilian of Austria had a new fortress built nearby, garrisoned with 250 footmen and forty horse - modern guns, modern times. But by the early 1500s the castle was already drawn on maps as a ruin.

Then came the war that erased the rest. The Eighty Years' War turned the Scheldt into a strategic prize, and in 1583 and 1584 Dutch rebels broke the dikes around Saeftinghe deliberately. They wanted to deny the Spanish any foothold north of Antwerp. When Antwerp fell to the Spanish in 1585, the rebels held the inundation. Salt water poured into Zeelandic Flanders and stayed. Polders, farms, the village of Saeftinghe, the harbor, the castle - all went under. The breach that opened near the castle, the Saeftinghse Gat, scoured a deep channel through the soft ground and washed away most of what was left of the walls. By 1584, the wikipedia article notes, much of the castle ruins had already been undone by their own moat, now a tidal trench.

The Drowned Land of Saeftinghe is now one of the largest brackish tidal wetlands in Europe, a protected nature reserve of around 3,500 hectares where you can hike on guided walks across gleaming mudflats. Spoonbills work the channels in summer. In autumn, the air shakes with the calls of thousands of geese. Visitors come for the silence and the scale - the strange beauty of a place that humans built, abandoned, and then deliberately gave back to the sea. The remains of Saeftinghe Castle were still visible above the mud until World War II, and were noted up to 1963. After that, they vanished from view. A castle built to tax the tide is now patrolled by the tide. The exact location is, as the records say, lost.