In Act 3.1, three main points take place. First, the conspiracy is in full swing, even if Cassius believes that the conspiracy has been detected. Trebonius gets Antony to leave, and Metellus goes asks Caesar to pardon his brother from exile. Caesar refuses, and he says his famous lines:
"I am constant as the northern star,
Of whose true-fix'd and resting quality
There is no fellow in the firmament."
Afterwards, the conspirators in earnest attack Caesar and stab him to death. Brutus stabs Caesar as well. Here is where Caesar says: “Et tu, Brute.” Upon the death of Caesar, the conspirators proclaim freedom and liberty.
Second, Antony hears about the death of Caesar, and he worries whether he will die as well. Brutus assures him that the conspirators will not kill him. Antony, at this point, addresses the deceased spirit of Caesar and asks for pardon for making peace with the conspirators.
Finally, Brutus allows Antony to address the people of Rome. Cassius says that this is a bad idea and that Antony will turn the people of Rome against the conspirators. Brutus still allows Antony to speak, but he will speak before Antony. Antony is left alone and prophesizes that civil war will come.