As far as lost islands go, Ferdinandea — about 19 miles (31 kilometers) off the southern coast of Sicily — is a particularly odd example. That's because throughout history, the island, which actually is the tip of a submerged volcano, has reappeared multiple times, only to disappear again beneath the waves before anyone can decide to which nation it belongs.
The first recorded emergence of Ferdinandea was in ancient times, when it rose above the waves after underwater volcanic eruptions during the first Punic War in 264-241 B.C.E. when the Romans and Carthaginians probably bickered about whom it belonged to.
In July 1831, thanks to more volcanic activity, Ferdinandea again appeared. It had a circumference of about 3 miles (5 kilometers) and rose about 213 feet (65 meters) above water level. Great Britain, Spain and the then-kingdom of Sicily all laid claim to it. Sicily's ruler Ferdinand II dubbed it Ferdinandea, after himself, while the British called it Graham Island, after James Graham, the second baronet of Netherby [sources: New York Times, Nethery].
Before they could resolve the matter, though, the island again sank below the water, six months after appearing. In 2002, heavy seismic activity made scientists think a re-emergence was likely. To get a jump on things, Sicilian divers planted a flag on the rock, hoping to claim it for Italy the minute it reappeared. But Ferdinandea stayed under water [source: The New York Times].