Cassius plays the major role in organizing the conspiracy that results in the assassination of Caesar. Cassius is clever in manipulating Brutus to join the conspiracy. He works on Brutus psychologically, appealing to his love for Rome, his sense of honor, and his ego, as well. Cassius emphasizes how great Caesar's power has become--a threat to Roman freedom--and he insists that Brutus is certainly as worthy as Caesar as a man and a leader. To further advance his purpose, Cassius plots with others already a part of the conspiracy to play upon Brutus' sense of responsibility to the people of Rome. He forges letters, supposedly to Brutus from Roman citizens, and arranges for them to be thrown into Brutus' window and displayed in the city. Cassius is sure of himself in his manipulation of Brutus. He tells his fellow conspirator Cinna the following:
Three parts of him
Is ours already, and the man entire
Upon the next encounter yields him ours.
Cassius' prediction is correct. Brutus does join the conspiracy, Caesar is assassinated, and Cassius' hidden agenda is achieved.