First settled by Greeks in the second millennium BC, Naples is one of the oldest continuously inhabited urban areas in the world. In the ninth century BC, a colony known as Parthenope was established on the Island of Megaride, later refounded as Neápolis in the sixth century BC. Naples' historic city centre is the largest in Europe and a UNESCO World Heritage Site, with a wide range of culturally and historically significant sites nearby, including the Palace of Caserta and the Roman ruins of Pompeii and Herculaneum. After the Expedition of the Thousand led by Giuseppe Garibaldi, which culminated in the controversial Siege of Gaeta, Naples became part of the Kingdom of Italy in 1861 as part of the Italian unification. The city is situated on the Gulf of Naples, on the western coast of southern Italy; it rises from sea level to an elevation of 450 metres (1,480 ft).