of Rome first, Cassius is self-interested. Cassius wants to assassinate Caesar because it personally annoys him that Caesar is so popular and rising above the rest of the senators. He does not want to bow down to a person who was once his equal, which he fears is about to happen.

Cassius knows, however, that killing Caesar is risky, which is why it is so important to have Brutus on board with the plot. Brutus has a sterling reputation and commands a great deal of respect. If he participates in the murder, he will lend legitimacy to the murderers.

Cassius, a cold-blooded (and somewhat cowardly) politician, works on Brutus' sense of worry that Caesar gaining too much power will be bad for Rome. He uses Brutus as a tool to help him achieve his own desires.

In the end, all of Cassius' plans come to nothing—recruiting Brutus backfires when Brutus, behaving honorably, allows Antony to address the crowd. Antony turns the crowd against the conspirators, starting a civil war that lead to both Cassius's and Brutus's defeat and death.

In the beginning of Shakespeare’s Julius Caesar, Cassius wants to control Brutus. In act 1, he effectively persuades Brutus to recognize Caesar’s growing power by appealing to Brutus’s patriotism and flattering his sense of nobility and honor. Cassius knows Brutus well and is aware of how easy it is to manipulate him. The manipulation works; Brutus is persuaded that Caesar must be killed, and thus, Brutus joins the other conspirators to plan Caesar’s death.

But once Brutus joins the conspiracy, the power in the relationship shifts. Brutus becomes the dominant leader as they make plans to kill Caesar. Once they have killed Caesar, it is Brutus who allows Mark Antony to speak at the funeral against Cassius’s wishes. Brutus is motivated by idealism, and he trusts Antony to be true to his word. But Cassius is much more practical, and he sees the dangers in allowing Antony to speak to the crowd. However, unlike in act 1, Cassius is unable to persuade Brutus to follow his advice. This leads to their downfall as Antony masterfully turns the people of Rome against the conspirators.

In act 4, Brutus and Cassius argue over their different approaches to running the war against Antony and Octavius. Brutus, ever the idealist, condemns Cassius for taking bribes. Cassius, ever the pragmatist, condemns Brutus for being so hard on him and not treating him like a true friend would. Their argument explodes until Cassius demands that Brutus kill him since Brutus no longer loves him. This dramatic moment reconciles the two friends, as they realize their hot words are not sincere. Brutus reveals that his wife has committed suicide, and as a result, it is hard for him to deal with the grief. Cassius feels guilt for having added to his troubles, and they drink a cup of wine to “bury all unkindness.”

Despite this reconciliation, Brutus still remains deaf to Cassius’s advice about their upcoming battle plans. Cassius realizes Brutus’s ideas will not work, but he goes along with his friend’s plan to march on the plains of Philippi. There on that battlefield, both friends meet their deaths. They are insistent upon dying with honor and in a way that they know would be respected by the other.

As was mentioned in the previous post, Cassius and Brutus are respected politicians, brothers-in-law, and co-conspirators. Cassius is a well-read politician who appeals to the other senators with the plot to murder Julius Caesar. Cassius first approaches Brutus in Act One, Scene 2 with the idea that Caesar plans to rule Rome as a tyrant. Cassius understands Brutus's noble character and appeals to his sense of duty to Rome. Cassius succeeds in convincing Brutus that murdering Julius Caesar is what is best for Rome. Brutus is close friends with Cassius and trusts his plan to assassinate Caesar. However, Brutus influences Cassius's decision to not kill Mark Antony along with Julius Caesar. After Caesar's assassination, Cassius joins forces with Brutus to challenge Antony, Octavius, and Lepidus. Despite their disagreements, Brutus and Cassius remain loyal friends throughout the play. They both risk their lives and reputations by murdering Caesar and fighting against Antony's and Octavius's troops. Tragically, both characters commit suicide during the final battle. 

Cassius and Brutus are brothers-in-law. But they are also senators and respected leaders in Rome, and this is the truly important aspect of their relationship. In Act I, Scene 2, Cassius first broaches the idea that Caesar is threatening to usurp the throne of Rome, ending the Republic. He appeals to Brutus's sense of patriotism as well as his personal pride by describing Caesar as a dangerous, designing man. All of this is intended to, in Cassius's words, be a "seduction" of Brutus. The "seduction," as it were, was a success. Brutus not only joined the conspiracy against Caesar, but he quickly became its leader, and, after his speech to the Roman people following the assassination, its public face.  It is their relationship as leaders of the conspiracy that is important to the development of the plot. They have a bitter argument in Act IV, Scene 3, but are reconciled, and both men die by suicide (with the help of their servants) after their armies are defeated at Philippi.

Cassius and Brutus are brothers-in-law who conspire to assassinate Julius Caesar toward the beginning of the play. Brutus is depicted as a relatively naive individual who gets taken advantage of by several characters in the play. In contrast, Cassius is portrayed as a shrewd politician, who is willing to do whatever it takes to prevent Caesar from becoming a monarch. Cassius knows Brutus rather well and cunningly manipulates him by mentioning how Caesar's ambition will harm the Roman citizens. Brutus inherently trusts Cassius enough to join the conspirators, who carry out a serious crime against the most powerful man in Rome. The fact that Brutus fully trusts his brother-in-law, and that Cassius thoroughly understands how to motivate him, indicates that the two characters are close allies and friends.

Before the final battle at Philippi, Brutus receives word that Cassius has been selling offices. Brutus is deeply hurt by this betrayal. Cassius and Brutus get into a serious argument but eventually reconcile with each other. Their ability to move forward following their argument illustrates their close bond and willingness to trust each other. While Cassius and Brutus do not share the same motivation, they support and work with each other throughout the play. Despite the fact that Brutus does not follow all of Cassius's suggestions, he is willing to conspire with him against Caesar and fight Octavius's and Antony's forces.

In my opinion, they're buddies that were driven apart by conflict.  Here's the best way I can describe it.  I played on a pretty good football team in college.  We should have finished the season undefeated, but at one point found ourselves losing in the second half.  All of us on the team were pretty good buddies at this point, as you normally are when you spend that much time together.  However, on the sideline of this game we just couldn't stop pointing fingers and complaining about what was happening.  This eventually led to our loss in that game.

This is how I see Brutus and Cassius.  They are obviously bonded strongly by friendship as we can see during their conversations in act one and their farewells at the end.  But when things started to look a little bleak, they really struggled with their own friendship.  They did manage to patch it up just in time to kill themselves, but that rift in act four had to be weighing on both of their minds.

I think even more than friendship, they probably respected each other's ideals.  Cassius certainly used this against Brutus to get his own means, but isn't that what friends do from time to time?  Granted this is a little worse than what we would consider day-to-day, but the principle is still the same.