Mistakes in the Series (CHB)

"They know this stuff and I have to really keep on top of this because if I do make a mistake or make a reference that’s wrong, they’ll catch me. They’re very perceptive about everything mythology."

- Rick Riordan

Despite Rick Riordan's best intentions, there are mistakes in the Percy Jackson and the Olympians series and The Heroes of Olympus series, either based on continuity or character flaws. While some of these have explanations, others do not and can only be considered mistakes.

The Lightning Thief

 * It is stated that the gods follow Western Civilization wherever it is strongest and are currently in the United States of America. Several important figures in American history are also mentioned to be demigods, including George Washington. However, America did not become a world power until almost a hundred years later.
 * This also creates other problems as well, as even if the gods had moved to America in the 1700's, the Empire State Building, the current location of Olympus, wasn't completed until 1931.

The Sea of Monsters

 * Thalia Grace appears in Percy's dreams during the story. In his dreams, she is described as having green eyes. However, when she is revived and appears in later stories, her eyes are said to be blue.
 * This could simply be because it was in a dream and that is how Thalia appeared, but this is unconfirmed.
 * Annabeth Chase told Percy that she knew parts of the Great Prophecy, but not the whole thing. Later, she mentioned knowing what the prophecy was and that it gave her nightmares.
 * While saving Blackjack from the Princess Andromeda, Percy calls Blackjack a mare (a female horse). However, Blackjack is a male in all other appearances.

The Last Olympian

 * Silena Beauregard's hair and eye color change from the color mentioned in The Demigod Files.
 * It is possible that because Silena is a daughter of Aphrodite, her hair and eye color can change naturally.

The Lost Hero

 * While Jason Grace was given a tour of the camp, it is said that all the new cabins were built last year. However, The Lost Hero takes place only 4 months after The Last Olympian, during the same year.
 * While Jason is fighting Porphyrion, he mentions being the leader of the First Legion. However, we find out in The Son of Neptune that Camp Jupiter is composed of the Twelfth Legion.
 * It is possible that Jason got this wrong as a result of his memories being stolen from him.
 * Rachel Elizabeth Dare is said to be going to Clarion Ladies Academy in New Hampshire. However, in The Last Olympian, Clarion Ladies Academy was in Connecticut.

The Son of Neptune

 * Percy yells at Hera for taking eight months of his life from him. However, Percy was only gone for six months, as he vanished from Camp Half-Blood on December 13th and then appeared at Camp Jupiter in late June.
 * Gaea told Hazel Levesque that Sammy died of a heart attack in the 1960s. However, it is revealed in The Mark of Athena that Sammy lived much longer, even seeing the birth of his great grandson Leo Valdez.
 * It is possible that Gaea was lying however.

The Demigod Diaries

 * The story Leo Valdez and the Quest for Buford mentions that Leo has been working on the Argo II for two months, despite this story taking place less than a week after the events of The Son of Neptune.

The Mark of Athena

 * Soon after the Argo II arrives at Camp Jupiter, it is mentioned that Hylla left earlier in the morning. However, Hylla was present in the Senate meeting when the Argo II first arrived at the camp.
 * Soon after the Argo II is forced to flee from Camp Jupiter, Percy sees sunset over a live feed of Camp Half-Blood. However at the time it was only early afternoon at the camp during the summer, making a sunset very unlikely.
 * Hazel Levesque mentions to Leo that she hadn't had a flashback in a long time. However, she only refrained from having a flashback for a few days at this point.
 * Alcyoneus states in The Son of Neptune that he must rise before any of his fellow Gigantes, as he is the oldest. However, Otis and Ephialtes have been helping Arachne capture demigods for centuries.
 * It is possible that Otis and Ephialtes never truly rose, as they made a home under the surface of Rome.
 * While talking to the Roman god Bacchus, he mentions how he fought along side Heracles. However, Heracles is the Greek name for the Roman god Hercules.
 * Percy mentions that he knew the Romans for weeks. However, by this point in the series he had only known the Romans for about ten days, including the time he spent with Frank and Hazel on his quest.
 * At one point, Leo Valdez sets his clothes partially on fire when he is woken up by a large ship. However, his clothes have been immune to fire every other time in the series.
 * Hercules warns Piper and Jason that he will kill them and their friends on the Argo II if they try and contact them. Later, when Piper thinks of a plan to pass Hercules without giving him the Cornucopia, she uses an Iris Message to contact them.
 * It is possible that Hercules simply didn't notice them message.