The Heroes of Olympus is a series of five adventure and fantasy novels written by Rick Riordan, an American author. It follows the "Percy Jackson & the Olympians" series and is followed by "The Trials of Apollo" series. The stories are based around Greek and Roman mythology. It describes the efforts of seven demigod heroes to prevent the earth goddess Gaea from waking up. The first book in the series was released on October 12, 2012 and the last one was released on October 7, 2014.