Märket is a bare rock in the sea between Sweden and Finland, with a border across it. In 1885 the Finns put a lighthouse on the highest point, which lay on the Swedish half. Sweden never treated the tower as Swedish, and for about a century the matter sat there. When the two countries finally tidied it up, they neither moved the lighthouse nor handed over the ground. They bent the line. It now wanders across the rock in a backwards S, about 480 metres of it, going around the tower so that no land changes hands overall and each country keeps the coast it had, along with the fishing. The lighthouse has run itself since 1979, and GPS has taken most of its work. What is left is an extremely careful border around a building ships hardly need, drawn by two neighbours who wanted the mistake fixed and the sums unchanged.