Final answer:
In the play 'Hamlet' by William Shakespeare, Horatio is reminded of Julius Caesar's assassination when he sees the ghost. This is an example of an allusion, a literary reference to another work.
Step-by-step explanation:
Horatio is reminded of the historical event of Julius Caesar's assassination when he sees the ghost in the play 'Hamlet' by William Shakespeare. This literary reference is called an allusion, which is when a work of literature references another work explicitly. In this case, the author is referring to the historical event of Julius Caesar's death to emphasize the ghostly presence in the play.