In Act 1, Scene 2, Caesar observes to Mark Antony that Cassius seems to be a wily political opponent, and his observations contain both dramatic irony and foreshadowing:
Let me have men about me that are fat,
Sleek-headed men, and such as sleep a-nights.
Yond Cassius has a lean and hungry look.
He thinks too much. Such men are dangerous.
Fear him not, Caesar; he’s not dangerous.
He is a noble Roman, and well given.
Would he were fatter! But I fear him not.
Yet if my name were liable to fear,
I do not know that the man I should avoid
So soon as that spare Cassius.
Caesar's sense for Cassius's political ambition is absolutely correct, of course: in anticipating his potential for ruthlessness, Caesar unwittingly foreshadows Cassius's instrumental role in the plot against him that will eventually lead to his assassination. As this is a historical play, Caesar's death is likely familiar to the audience as a historical event—nonetheless, Shakespeare seizes upon this opportunity to stoke the ironic potential of the moment: Antony denies Cassius’s danger and advocates on behalf of the man, even as Caesar suspects (and the audience knows) that Cassius could plot against him. Caesar, for his part, dismisses this concern and follows Antony’s lead, insisting that he has no fear of Cassius—Caesar constantly asserts his manhood in Julius Caesar, and this sequence is no exception.
Shakespeare uses passages like these to toy with the audience's sense of suspense and the possibility that Caesar—if he were just a bit more perceptive—would be able to avoid his death. It is never quite clear whether or not Caesar’s fate is preordained: even he himself can see that something is coming, and yet Antony seemingly allows it to happen by absolving Cassius of any criticism.
In Act 1, Scene 2, soothsayer calls out from the crowd and utters his famous warning to Caesar to "beware the ides of March." This is an explicit moment of foreshadowing and a setup for some rich dramatic irony:
Beware the ides of March.
What man is that?
A soothsayer bids you beware the ides of March.
Set him before me. Let me see his face.
Fellow, come from the throng.
Look upon Caesar.
What sayest thou to me now? Speak once again.
Beware the ides of March.
He is a dreamer. Let us leave him. Pass.
A mysterious soothsayer warning Caesar to beware the ides of March is an obvious example of foreshadowing. But this sequence also sets up the dramatic irony that will persist through to Caesar's assassination: Cassius, who asks the Soothsayer to repeat himself, is the very architect of the reason the Soothsayer warns Caesar in the first place. Caesar will keep Cassius close even as the audience grows increasingly familiar with Cassius's intentions and his conspiracy against Caesar, until it is too late.
Caesar displays his typical masculine arrogance in dismissing the Soothsayer as a "dreamer"—the first in a long line of warnings Caesar will dismiss up until his death as he attempts to enforce his masculinity and preserve his image of unassailable stability. Julius Caesar is one long exploration of the dangers of pride in a society constructed on manhood and honor, and Caesar is the central example of how deadly arrogance can be.
In Act 2, Scene 2, as the threat against Caesar grows, Calpurnia reports a frightening dream to her husband in an effort to keep him from leaving the house. Calpurnia's report of these new omens continue Shakespeare's dramatic sequence of foreshadowing Caesar's death, while Caesar's stubborn ignorance builds dramatic irony for the audience:
Caesar, I never stood on ceremonies,
Yet now they fright me. There is one within,
Besides the things that we have heard and seen,
Recounts most horrid sights seen by the watch.
A lioness hath whelpèd in the streets,
And graves have yawned and yield up their dead.
What can be avoided
Whose end is purposed by the mighty gods?
Yet Caesar shall go forth, for these predictions
Are to the world in general as to Caesar.
Witness to a long list of omens and a fair share of soliloquies, there is no doubt for the audience as to what is at stake as Caesar continues to refuse to listen to the world around him. In Caesar’s view, however, gods will do what they do—he might as well continue to live life unburdened. Caesar does not appear to believe that he has much agency in his determining his fate, and his attitude continues Shakespeare's paradoxical exploration of human decision-making in a classical world of predestination to an especially frustrating conclusion. It would appear, at least to the audience, that Caesar's stubbornness leads him to directly his death. His insistence in staying his course feels more like arrogance than genuine submission to the gods' will.
In Act 2, Scene 3, Artemidorus reads aloud a letter he has written warning Caesar of the conspiracy against him and heightens the dramatic irony for the audience:
Caesar, beware of Brutus, take heed of
Cassius, come not near Casca, have an eye to Cinna,
trust not Trebonius, mark well Metellus Cimber.
Decius Brutus loves thee not. Thou hast wronged
Caius Ligarius. There is but one mind in all these
men, and it is bent against Caesar. If you beest not
immortal, look about you. Security gives way to
conspiracy. The mighty gods defend thee!
In this letter, Artemidorus spells out the entire scope of the threats to Caesar borne by his supposed allies and peers. By including this scene, Shakespeare both foreshadows Caesar's assassination and establishes the beginning of a long chain of dramatic irony to come: Artemidorus, just like the audience, knows full well that Caesar's life is at risk and tries to inform him before it is too late; Caesar's death may be preventable. Shortly hereafter, in Act 3, Scene 1, the dramatic irony will reach its peak when Caesar refuses to read the letter.
The inclusion of this short scene heightens the tensions of the play and gives the audience a false sense of security. Shakespeare will continue to stoke suspense with Caesar's continued obliviousness in the face of increasingly obvious omens and several urgent attempts to alert him to his impending death. Throughout the first half of Julius Caesar, it is unclear whether or not there is any alternative to Caesar's assassination: is the man's fate guaranteed, or can he escape it? The question of Caesar's agency in avoiding his demise lies at the heart of Shakespeare's exploration of the power of human decision-making to change one's destiny.