beseeming ornaments,

To wield old partisans, in hands as old,

Canker'd with peace, to part your canker'd hate:

If ever you disturb our streets again,

Your lives shall pay the forfeit of the peace.

The Prince declares that anyone who breaks the peace between families will pay with their lives, a threat that ultimately he does not follow through on when he banishes Romeo, instead of executing him, after killing Tybalt; however, it is one that does come true in the eventual death of Romeo and Juliet both. Ironically, the death of the young couple is what finally brings about peace, rather than disturbs it.

Later, in Act I, Scene iv, Romeo himself has a premonition of sorts about the events to come:

I fear, too early: for my mind misgives
Some consequence yet hanging in the stars
Shall bitterly begin his fearful date
With this night's revels and expire the term
Of a despised life closed in my breast
By some vile forfeit of untimely death.
But He, that hath the steerage of my course,
Direct my sail! On, lusty gentlemen.

His concerns about fate and misfortune here can certainly be said to foreshadow the tragedy to come.

Certainly, the concern that Romeo expresses at the end of Act 1, scene 4, before he and his friends go to the big party at Lord Capulet's house foreshadows later tragedy in the play.  He says that his

mind misgives
Some consequence yet hanging in the stars [that]
Shall bitterly begin his fearful date
With this night's revels, and expire the term
Of a despised life closed in [his] breast
By some vile forfeit of untimely death.  (1.4.113-118)

In other words, Romeo has a sort of premonition that the party tonight will initiate some series of fated events in his life that will culminate in his death as a young man.  He, of course, is right.  Tonight, he will meet Juliet and begin the relationship that will eventually lead to his suicide in her family's vault.

When Romeo and Juliet first meet and kiss, the audience knows that they are sworn enemies, although they do not know one another's identity yet.  Juliet calls him "Good pilgrim," in part, because she does not know his name, and Romeo calls her "dear saint" (1.5.108, 1.5.114).  It is only after this first encounter, where they fall in love at first sight, that each learns the other's identity.  Their initial meeting when they do not know the other's identity constitutes dramatic irony because we know that they are sworn enemies before they realize it.

Later, in Act 2, scene 2, when Juliet believes that she is alone and speaking only to herself on her balcony, we know that Romeo is there, hidden by the darkness, and that he can hear everything she says.  Because we know more than she, this is another example of dramatic irony.

In Act II, scene iii, Friar is speaking of the power of plants when he notes that the plant has several powers. Plants can be medicinal, and they can be poisonous. As he finishes he uses a metaphor that foreshadows the death of lovers as they are products of kings:

Two such opposed kings encamp them still
In man as well as herbs, grace and rude will;
And where the worser is predominant,
Full soon the canker death eats up that plant.

Later, in scene iv, Mercutio and Benvolio are talking about Romeo when Mercutio notes that Romeo's love for Rosaline is killing him. Little does Mercutio know that Romoe's love is not for Rosaline, but for Juliet, and that her love will literally kill him:

Alas poor Romeo! he is already dead; stabbed with a
white wench's black eye; shot through the ear with a
love-song; the very pin of his heart cleft with the
blind bow-boy's butt-shaft

Mercutio uses language figuratively here as hyperbole or exaggeration, but the foreshadow is clear. Love will kill Romeo.

When Romeo sneaks into the garden beneath Juliet's balcony, he overhears her speaking to herself about him. After he reveals his presence to her, she expresses her concern that her family would kill Romeo if they found him there. He responds, "My life were better ended by their hate / Than death prorogued, wanting of thy life" (2.282–83). In other words, he says that he would rather die a quick death than to live a long life without her love. This foreshadows Romeo's actual death later in the play. When he believes that Juliet has died, he takes his own life with a vial of poison rather than survive and have to live without her.

Romeo is put in that position in the first place because Tybalt, Juliet's cousin, challenges him to a duel. In his hatred of Romeo, Tybalt seeks Romeo the day after the party at Lord Capulet's, though Romeo refuses to fight him because he has just married Juliet. When Mercutio steps up to fight Tybalt, believing Romeo to be acting like a coward, Tybalt kills Mercutio, and so Romeo kills Tybalt. Thus, indirectly, Romeo's life is brought to an end as a result of Tybalt's hate, just as he said he would prefer rather than living a long life without Juliet.

Act 2, scene 3 begins with a soliloquy delivered by Friar Laurence. In this soliloquy he talks about the plants he is growing, and about the medicinal and poisonous properties of those plants. He says that the medicine derived from one plant can be poisonous if administered in the wrong dose, just as the poison from another plant might be medicinal if administered in the right dose. The broader point here is that something good can turn into something bad if it is taken in the wrong dose. Or, as Friar Laurence puts it:

Virtue itself turns vice, being misapplied;
And vice sometimes by action dignified.

This idea can be applied to the love between Romeo and Juliet, and indeed foreshadows what becomes of that love. Their love is a good thing, which, like medicine, makes them feel better, but because they love too intensely, it becomes poisonous and ends in tragedy.

In act 2, scene 6, just before Romeo and Juliet are married, Friar Laurence says to Romeo:

These violent delights have violent ends
And in their triumph die, like fire and powder.

Here, Friar Laurence is warning Romeo not to love too violently or recklessly. He says that emotions or "delights" which are too "violent" will inevitably lead to "violent ends." Romeo and Juliet are guilty of loving too violently because they are impatient and infatuated with one another. They consider only their love and nothing else. In the second part of the quote, Friar Laurence compares this type of reckless love to "fire and powder," meaning gunpowder. The image evoked here is of a trail of gunpowder set alight, culminating in a violent explosion at the end of the trail. This is a fitting analogy for Romeo and Juliet's love, and foreshadows the violent, tragic end to which their love eventually comes.

Act 2 of Shakespeare's Romeo and Juliet is a treasure trove of foreshadowing. It's as if Shakespeare couldn't resist telling us what's going to happen to the star-crossed lovers so that we anticipate every moment of their short lives together.

In act 2, scene 2, the famous balcony scene, Juliet expresses her fear for Romeo's safety:

JULIET: How cam'st thou hither, tell me, and wherefore?
The orchard walls are high and hard to climb,
And the place death, considering who thou art,
If any of my kinsmen find thee here.
. . . If they do see thee, they will murder thee. . . .
ROMEO: I have night's cloak to hide me from their eyes;
And but thou love me, let them find me here.
My life were better ended by their hate
Than death prorogued, wanting of thy love. [2.2.66–82]

Romeo says that he would rather die quickly at the hands of the Capulets than to live a long life without her love. At the end of the play, thinking that Juliet is dead, Romeo chooses to take his own life rather than live without her.

At the end of scene 2, Juliet speaks the words that everyone knows, but not before hinting at what's to come in their relationship.

ROMEO: I would I were thy bird.
JULIET: Sweet, so would I.
Yet I should kill thee with much cherishing.
Good night, good night! Parting is such sweet sorrow,
That I shall say good night till it be morrow. [2.2.195–199]

In Friar Laurence's cell in scene 3, when the Friar agrees to marry Romeo and Juliet, Romeo urges him to marry them as soon as possible.

ROMEO: O, let us hence! I stand on sudden haste.
FRIAR LAURENCE: Wisely, and slow. They stumble that run fast. [2.3.96–97]

Since they first met, Romeo and Juliet have been running very fast into their relationship, which only hastens their deaths.

Back in Friar Laurence's cell a few scenes later, Romeo and Juliet are about to be married. Friar Laurence says he hopes all will be well, and Romeo speaks some fateful words.

FRIAR LAURENCE: So smile the heavens upon this holy act
That after-hours with sorrow chide us not!
ROMEO: Amen, amen! But come what sorrow can,
It cannot countervail the exchange of joy
That one short minute gives me in her sight.
Do thou but close our hands with holy words,
Then love-devouring death do what he dare—
It is enough I may but call her mine. [2.6.1–8]

"Love-devouring death" does, in fact, do "what he dare," and Romeo chooses to end his life to "call her mine" forever.

Whenever one is asked to find evidence of foreshadowing in Shakespeare's Romeo and Juliet, look to the Prologue, Chorus, or Romeo's dialogue for answers. The Chorus is the voice of Fate which is like an omniscient narrator guiding the audience along through the warnings at the beginning of acts. Romeo is very in tune with Fate and has dreams that he feels warn him about the future. Both of these are places where foreshadowing is found. For example, the Chorus explains the current situation at the beginning of act 2 and explains that lovers usually have time and means to meet to express "vows" to each other, "but passion lends them power, time means, to meet,/ Temp'ring extremities with extreme sweet" (II.Prologue.13-14).

Another quote that has foreshadowing elements happens before Romeo and Juliet are married and Romeo is talking with Friar Lawrence: "The love-devouring Death do what he dare;/It is enough I may but call her mine" (II.iv.7-8). It's as if with this quote Romeo is tempting death or fate to intervene!

The foreshadowing/irony that opens act V of Shakespeare's tragedy Romeo and Juliet comes in the form of a monologue delivered by Romeo, while he is in exile, about a dream he had that has put him in a wonderful mood and made him believe that he may soon be receiving wonderful news. He describes the dream that has so lifted his spirits as follows:

"I dreamt my lady came and found me dead—
Strange dream, that gives a dead man leave
to think!—
And breathed such life with kisses in my lips,
That I revived, and was an emperor."

This dream is a vision of the exact opposite of what will happen at the end of the play, and thus it serves as both foreshadowing and irony. Ultimately, it is Romeo who will find Juliet "dead," and rather than kiss her back to life, he will take his own life before she has a chance to revive.

There is a more immediate irony at work in this scene as well. Just following the lines in which Romeo predicts he will be getting good news soon, Balthazar arrives and delivers the (false) news of Juliet's death. While Romeo was right that he would soon be receiving a message from Verona, he could not have been more wrong about what the content of that message would be.