In Greek mythology, the questions of what should be remembered and why are especially central in Homer’s The Odyssey, which is believed to have been composed orally before the creation of written language in the Greek world. In such a culture, memory is especially significant, as it’s the only way to preserve and transmit cultural values, beliefs, and events. Forgetting can be deadly; it can cause people to lose their way, literally (they forget where their home is) and figuratively (they forget where they belong). However, certain memories can be harmful, causing excess grief, which fuels conflict, as when Menelaus remembers a story of Helen betraying her people. In Virgil’s Roman epic Aeneid, Aeneas refuses to spare Turnus when he notices the warrior wearing the sword belt of Aeneas’s friend, whom Turnus killed.

Riordan incorporates the problem of memory in several ways. Both Jason and Percy had their memories taken from them to enable them to switch camps. Attempting to recover those memories is what brought the Roman and Greek camps into contact. Characteristically, memory can be both harmful and beneficial, depending on what is being remembered.