The Sky Palace and other amazing sights in the world's forgotten cities

Founded, flourished and eventually forgotten – this has been the fate of many cities since ancient times. A few names have stayed alive in legend and literature while others disappeared completely – until a chance discovery brought these mysterious metropolises back from the dead. From Sigiriya, the amazing hill-top site in Sri Lanka, to the astonishing Pompeii in Italy, we look at some of the most fabulous cities lost and reborn plus how to visit, when it's safe to do so.