Anachronism is when something happens or is attributed to a different era than when it actually existed. This is usually a mistake, such as an author writing a period piece and accidentally using language that’s too modern. However, it can also be intentionally used as a literary device, if the author wants to comment on a theme like time or society. Example: Cassius in Julius Caesar says that 'the clock has stricken three,' even though mechanical clocks had not been invented in 44 A.D