The Concrete Island That Held 5,259 People in 1959

From a passing ship in the 1920s the island looked enough like the battleship Tosa that Nagasaki sailors started calling it Gunkanjima -- warship island. A pale slab of concrete tenements rising straight out of the East China Sea, edges sheared off as if cut with a knife.

Coal had been found on the seabed under Hashima around 1810, but the place was not a city until Mitsubishi Goshi Kaisha bought it in 1890 and started sinking shafts. To house the miners they reclaimed land outward from the original rocky outcrop and ringed the whole 16 acres in a concrete seawall. In 1916 they built Japan's first large reinforced-concrete apartment block -- nine stories of company housing, because typhoons would have ripped wood off the rock.

By 1959 there were 5,259 people on it. About 83,500 per square kilometre, roughly nine times Manhattan's density, and at that moment the highest on Earth. The island ran an elementary school, a junior high, a hospital, a Shinto shrine, a cinema, public baths, and a pachinko parlour. Children walked to class along rooftop corridors because the alleys at ground level were too narrow.

Then Japan switched fuels. Cheap imported petroleum displaced domestic coal through the 1960s. Hashima's shafts closed in January 1974, and by April 20 every remaining family was on a boat to the mainland. Apartments were left with the dishes in the sinks.

UNESCO inscribed it in 2015 as part of the Sites of Japan's Meiji Industrial Revolution -- a listing South Korea and China fought hard, pointing out that Korean and Chinese conscripts had been worked in the wartime mines. The seawall still holds. The buildings, mostly, do not.