Anachronism

Definition:

1. General: Something or someone that is placed in the wrong historical period, especially a thing that belongs to an earlier or later time than that in which it exists.
2. Literature/Art: An error in chronology, where an event, object, custom, or person is placed outside its proper historical time—such as a wristwatch in a movie set in ancient Rome.

Example: The film included the anachronism of a Viking warrior using a modern-day compass.