After the Percy Jackson and the Olympians series Rick Riordan continued it with a follow up series called The Heroes of Olympus series, which has not yet ended, but has three books so far. In this series it introduces a roman camp like camp half-blood, only the roman's see the gods differently, in their roman forms. Normally the two camps would have fought( if they knew about each other), but the Greek kids try to make peace. However an evil possessive spirit takes control of one of the kids an shots the roman camp!!! Now seven half-bloods need to answer a prophesy, go to Rome, and fight something even more sinister that even the titans! This is a great follow- up to the Percy Jackson and the Olympians series. If you want to read it the first book is The Lost hero.