The ruined silhouette of the Parthenon on its hill above Athens is one of the world's most famous images. Its 'looted' Elgin Marbles are a global cause celebre. But what actually are they? In the first of an occasional 'series' on wonders of the world - such as the Colosseum, Stonehenge, the Pyramids, the Alhambra, Mary Beard, biographer, reviewer and leading Cambridge classicist, tells the history and explains the significance of the Parthenon, the temple of the virgin goddess Athena, the divine patroness of ancient Athens: