No contemporary account of the disaster survives, which is why the argument lasted so long. What does survive is paperwork. The Danish crown's land register, the Waldemar Erdbuch, records the district of Edomsharde as a place of substance. A will drawn up in 1345 names Rungholt outright. Best of all, there is a trade agreement between Rungholt and merchants of Hamburg dated 1 May 1361 - signed and filed eight months before the water came. That single document does more work than any legend: Rungholt was a going concern, with something worth trading and someone in Hamburg willing to sign for it. The archaeology agrees: roughly thirty per cent of the pottery recovered here is imported, an extraordinary proportion for a marsh village, including Rhenish stoneware and one vessel that travelled from Moorish Spain. The living came from cattle, from rye on ridged fields, and from boiling salt out of the peat.

Rungholt stood on Strand, a large low island in what was then the Danish Duchy of Schleswig. The 1362 storm tide - the Second Marcellus Flood - swept the whole southern North Sea coast, and estimates for the total dead run to around twenty-five thousand. Perhaps thirty settlements went. The coastline shifted east and left the fields, the dikes and the drowned behind it under tidal water. What remained of Strand was finished by the Burchardi Flood of 1634, and its fragments are the map of North Frisia today: the Nordstrand peninsula, Pellworm, Nordstrandischmoor, and the little Hallig of Suedfall sitting alone in the flats above where the town had been. Nobody rebuilt. The sea kept the ground.

Legends need a vacuum, and the silence of the sources gave them one. The seventeenth-century chronicler Matthias Boetius passed on local oral tradition, misdating the catastrophe to around 1300. His contemporary Anton Heimreich wrote down the story that stuck: drunken farmers of Rungholt caught a pig, poured drink into it, and demanded that the parish priest give the animal the last rites. The priest fled with the sacrament, dreamed a warning, and the flood came as judgement. The tale was not even original - it follows a story in Caesarius of Heisterbach's Dialogus miraculorum, attached to an earlier flood entirely. Theodor Storm, in his 1871 novella Eine Halligfahrt, gave the drowned town stately gabled houses, towers, mills and ships loaded with the treasure of the world. Then came Detlev von Liliencron's ballad Trutz, blanke Hans, written in the 1880s, whose opening line every North German schoolchild once knew: Heut bin ich ueber Rungholt gefahren. After that the fiction was fixed, and sailors said you could hear the church bells under the keel on a calm night.

The evidence came back the way it had gone, on the tide. From 1921 into the late 1930s, scouring currents stripped the silt north of Hallig Suedfall and exposed what lay beneath: dwelling mounds, dike lines, wells, cisterns. A local farmer and surveyor named Andreas Busch walked out to them again and again, measuring structures the next spring tide might erase. Two timber sluices were the prize. The older measured about 20.5 by 3.3 metres, the newer 25.5 by 5.36 metres, and radiocarbon dating later placed them around 1200 and 1280 - hydraulic engineering of real ambition, built by people who knew exactly how precarious their ground was. Counting the wells, Busch put the population at fifteen hundred to two thousand across some sixty mounds behind a defensive dike. That is no metropolis - medieval Hamburg held perhaps five thousand - but for this coast it was substantial, and Busch's figures have held up well.

In 2023 a team from the universities of Mainz and Kiel, working with the state archaeological office of Schleswig-Holstein, took magnetic gradiometry and other geophysical instruments onto the flats and mapped ten square kilometres of seabed without digging. Announced through the German Research Foundation, the results amounted to a town plan: at least fifty-four dwelling mounds, drainage systems, a sea dike with a sluice harbour, a harbour basin to the south, two smaller church buildings - and the foundation of a main church forty metres by fifteen, brick-built, with a broad tower and a rounded apse. A church that size, comparable to the one at Breklum, was not built for a hamlet. None of this makes the pig story true or the bells real. It does something better. It replaces a morality tale about wealth and punishment with a community of farmers, salt-boilers and traders who held the North Sea off for generations, and who lost, on one January night, the argument everyone on this coast eventually loses.