In ACT I SC I the Soothsayer says to Cesar "Beware the Ides of March" ( I : i : In 18) . Cesar ignores the fat that he said that. Soothsayer walks away menacingly.
ACT IV SC I
In ACT I SC I Portia is worried about Brutus Because he is worried. Brutus refuses to tell Portia. Portia says "As it hath much prevailed on your condition, I should not know you Brutus" ( II : i : In 254-255). Brutus says he will tell her after he gets back.
ACT V SC V
In ACT III SC I Caesar is killed by the hands of the conspirators. Mark Antonty runs away and hides in his home. As said by Trebonius " Fled to his house amazed. Men, wives, and children stare, cry out in run, As it were doomsday" (III:i:In 97-99)
In ACT IV SC I Antony, Octavius, and Lepidus converse about a plan. Antony sends Lepidus on a mission. Antony tells Octavius "This is a slight unmeritable man, meet to be sent on errands" (IV:i: In 12-13). Octavius thinks he is a tried valiant solider.
In ACT V SC V Brutus impales himself on a sword. The person holding the sword was Strato. Brutus said " Caesar, now be still;" ( V:v: In 50). Then Brutus jumped on the sword. Antony thinks he is an honorable man.
The reason i think this is the theme is that, the most important person is killed. I mean what was Shakespeare thinking when he killed off the main character. The story is about him. "The Tragedy of Julius Caesar" (0:0 cover of the book) is the name of the story for Christs sake.