The Island Split in Half by an Accidental Border
Sweden and Finland share a tiny Baltic island — but the border bends around a lighthouse placed on the wrong side in 1885.
Märket is a low granite island in the Sea of Åland, about one kilometer long and 300 meters wide. Finland owns the eastern half; Sweden owns the western. The border between them does not run in a straight line.
In 1885, when Finland was a Russian grand duchy, Russian authorities built a lighthouse on Märket. The problem was discovered later: the lighthouse had been built on the Swedish side of the border. Neither country could simply move the lighthouse, and neither wanted to cede the lighthouse to the other.
The solution, negotiated and formalized in 1985, was to redraw the border around the lighthouse. Instead of a straight line, the border now bends in an S-curve — so that Finland, which owns the lighthouse side, took a piece of Swedish territory in the north to compensate Sweden for the piece it lost in the south. Total land area on each side remained equal. The border added two extra turning points to correct a century-old surveying mistake.
Märket has no permanent residents. The lighthouse is now automated. The island is uninhabited except for migratory birds and, occasionally, researchers. But it appears on every map of the Swedish-Finnish maritime border as an oddly curved line through a rock that almost nobody has visited.
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