A prophecy central to the Heroes of Olympus series, foretelling that seven demigods (Greek and Roman) will unite to prevent Gaia (the Earth Mother) from waking and destroying civilisation. The seven are Percy Jackson, Annabeth Chase, Jason Grace, Piper McLean, Leo Valdez, Frank Zhang, and Hazel Levesque. The prophecy's fulfilment requires the unprecedented cooperation of the rival Greek and Roman camps.