In Act I, there are instances that suggest Caesar's ambition:
1. As the Roman citizens await the arrival of the the mighty Caesar in Scene 1, Marullus intimates that Caesar has been inordinately ambitious because he has defeated Pompey's sons when he at one time was closely associated with Pompey as part of a triumvir:
And do you now put on your best attire?
And do you now cull out a holiday?
And do you now strew flowers in his way
That comes in triumph over Pompey's blood? (1.49-52)
2. In Scene 2, a scene in which Cassius strives to convince Brutus of the tyranny of Julius Caesar and his ambition, Cassius informs Brutus that Brutus has not seen the most respected citizens of Rome "groan[ing] underneath this age's yoke" (1.2.61). Further, Brutus describes his lowly position as "a wretched creature," but Caesar "Is now become a god." Cassius tells Brutus:
Why, man, he doth bestride the narrow world
Like a Colossus, and we petty men
Walk under his huge legs and peep about....(1.2.135-137)
Ay, marry, was't, and he put it by thrice, every time gentler than other, and at every putting-by
mine honest neighbours shouted
After Caesar and his train depart, Brutus talks with Casca, who describes Caesar as having been offered a crown by Marc Antony, but he refused it, although he appeared to desire it.
Ay, marry was't, and he put it by thrice,
every time gentler than other,
and at every putting-by
mine honest neighbours shouted (1.2.321-324)
It is those convincing words of Cassius and Casca that lead Brutus to join the conspirators who wish to assassinate Julius Caesar. He feels that Caesar is so greedy for power that he will become a tyrant, and his becoming an emperor will lead them to misery.
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