Today, March 15, is known historically as the Ides of March. This is because, as legend has it, Julius Caesar was warned by a soothsayer to "beware the Ides of March." It was this day that Julius Caesar was stabbed 23 times by the entire Roman senate. To commemorate this day, it would seem most appropriate to talk about Shakespeare's Julius Caesar play.
Interestingly enough, Julius Caesar (despite being the title of the play), is not the main character. In fact he only appears in three scenes and is killed in the beginning of the third act. The real central character of the play is Marcus Brutus, who was a great friend of Caesar but whom ultimately betrayed him.
Many of Shakespeare's historical plays correlate with some sort of Elizabethan sentiment or topic of the time. In this case it is a clear reflection of the anxiety within England over the succession of the crown since Elizabeth had refused to name a successor which had people worried that England might break out into Civil War similar to the one in Rome, after her death. The play was most likely premiered in 1599.