<Tr> <Th> Preceded by </Th> <Td> Percy Jackson & the Olympians </Td> </Tr> <Tr> <Th> Followed by </Th> <Td> The Trials of Apollo </Td> </Tr> <P> The Heroes of Olympus is a pentalogy of adventure, mythological fiction and fantasy novels written by American author Rick Riordan that collectively form a sequel series to the Percy Jackson & the Olympians series . This series details a conflict between Greek and Roman demigods and Gaea, the earth goddess . Riordan introduces Roman mythology into his sequel series as well as several new characters . The first book of the series, The Lost Hero, was published on October 12, 2010 . The final entry in the series, The Blood of Olympus, was published on October 7, 2014 . </P> <P> The plot of the Heroes of Olympus is centered around a prophecy, introduced in The Last Olympian, that predicted seven demigods would unite to protect the earth from Gaea . Demigods from both the Greek camp, Camp Half - Blood, and a newfound Roman camp, Camp Jupiter, work together to save the world from being destroyed by Gaea . The prophecy reads: </P>

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