The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings.
...when I tell him he hates flatterers,
He says he does, being then most flattered.
Cry, 'Havoc!' and let slip the dogs of war.
I come to bury Cæsar, not to praise him.
The evil that men do lives after them;
The good is oft interred with their bones.
This was the most unkindest cut of all
His life was gentle, and the elements
So mix'd in him that Nature might stand up
And say to all the world, 'This was a man!'
So, call the field to rest; and let's away
To part the glories of this happy day.
A Roman's gotta do....
This play ought to be called Brutus, since the central theme concerns that character's decision to join an assassination conspiracy and the repercussions of his action. Julius Caesar is dispensed with by the halfway point.
However, Caesar's assumption of the Roman dictatorship after the civil war fought against his former triumvirate partner Pompey and his victories in battle celebrated in the first scene of Shakespeare's play make him the most famous historical character of this period. In the play, the republican conspirators fear he will also allow himself to be crowned king. This fear may seem strange to us, since Caesar already had supreme power, but a kingship would usher in imperial power with an hereditary leadership, as opposed to the existing system in which the nobility chose who would rule. You can see that political terms such as "republican" had a slightly different meaning in those days.
But if Brutus, Cassius and the gang killed Caesar to remove a tyrant and to preserve what they considered democracy, then why are they the bad guys in Julius Caesar?
The plot of the play, like the storylines for Shakespeare's other Roman tragedies, was taken from Plutarch's Parallel Lives, written over a hundred years after the assassination, during the height of the imperial power in Rome that did indeed succeed the republic—at a time when Caesar and his heirs were greatly admired. Also Shakespeare was writing in England during another greatly admired British monarchy, Queen Elizabeth I, whose aging was giving rise to fears about battles over succession.
Sometimes, it seems the only thing Shakespeare considered worse than a bad ruler was the killing of a bad ruler.
But Brutus is not shown in as dim a light as his co-conspirators. He agonizes over the decision to murder Caesar. Both his good intentions and his political naivety are take advantage of by Cassius who lures him into the conspiracy and later by Mark Antony, who turns the tables against Brutus and Cassius. (Writing of Brutus's internal conflicts may have been practice for Shakespeare's creation of his next and greatest protagonist, the haunted Hamlet.) Rather than being portrayed as a bad man, Brutus for Shakespeare is a good man who did a bad thing for good reasons. He is moreover surrounded by characters of less honour. The conspirers Decius and Cassius are deceivers, both of others and of themselves, although Cassius becomes a more sympathetic as, in the face of impending defeat, he makes up with Brutus and faces his own demise honourably. Mark Anthony is cunning and power-hungry. Only Brutus remains a completely sympathetic character and upon his death he is eulogized by Antony as the "noblest Roman of them all". (Of course, Antony had previously eulogized Caesar as the "noblest man that ever lived".)
All in all, Julius Caesar is morally a somewhat confusing play. Which may be Shakespeare's point: morality is a shifting battlefield. It is often said this is a play about loyalty, but even this virtue is not an absolute, for loyalties also clash in Julius Caesar without providing a guide through the contradictions. Loyalty to leaders versus loyalty to the people. Loyalty to family versus loyalty to political ideals. Loyalty to competing friends and lovers.
With the ethical morass into which the protagonists fall, the play is a precursor to Macbeth, but in that later drama the confusion of fair and foul is eventually put right. The protagonist Macbeth is also a more typical Shakespearean tragic figure in that a fatal flaw—overweening ambition—brings him down. Brutus has no such driving character flaw. His downfall comes about because he didn't have Antony killed when he could have and because he trusted others. He'd make a good study for one of those modern pop-psychology books with titles like Why Good People Do Stupid Things.
It's also mildly interesting that many of the phrases from Julius Caesar that have become well-known are rather meaningless out of context:
"Beware the ides of March"
"Et tu, Brute"
"Cry 'Havoc!' and let slip the dogs of war"
"Not that I lov'd Caesar less, but that I lov'd Rome more"
"Friends, Romans, countrymen, lend me your ears"
"I come to bury Caesar, not to praise him"
Of greater application are:
"The fault, dear Brutus, is not in our stars, But in ourselves"
"There is a tide in the affairs of men Which, taken at the flood, leads on to fortune"
"The evil that men do lives after them; The good is oft interred with their bones"
The latter was spoken by Antony deceptively of Caesar, but applies more truthfully to Brutus. Perhaps the most telling statement is that of Antony at the end concerning his opponent:
His life was gentle; and the elements
So mix'd in him that Nature might stand up
And say to all the world 'This was a man!'
For me, this is Shakespeare's ultimate message in Julius Caesar. However, confused and contradictory is human nature, it is what we are and overall it is a wondrous thing. For all his terrible mistakes, Brutus is someone we can look up to as an epitome of humanity.
Don't worry, Antony gets his deserts in the sequel, Antony and Cleopatra.