There are several petitions presented to Caesar when he arrives on March 15 (the Ides of March) at the senate. One in particular pleads for mercy for Cimber's brother to be allowed home from banishment. Caesar responds with a resounding "No."
The letter given to him by Artemidorus listing all the conspirators' names and that Caesar should avoid them. The letter is put last as Caesar says he will deal with personal business after that of the state.
Irony abounds here since Caesar would have saved his own neck twice--the petitioner knew Caesar's answer would be "No" and this acted as a signal for the conspirators to attact.
The letter with his enemies names written in it, had Caesar opened it first, would have given him an advantage to leave the senate and go home to his wife unharmed.
Immediately before the assassination, Metellus Cimber presents a petition to Caesar, requesting that his brother, Publius Cimber, be allowed to return to Rome from his banishment. Caesar refuses, comparing himself to the North Star which is fixed and constant:
"...and that I am he
Let me a little show it, even in this:
That I was constant Cimber should be banished
And constant do remain to keep him so." (Act III, scene i)
In Act III, after refusing to heed the omens Calpurnia reports to her husband, Caesar insists that he will go to the Capitol. Once he is there, Caesar is presented with petitions.
Artemidorus steps up to Caesar and hands him the warning that he has read aloud in Act I, Scene 3. This paper is a letter to Caesar warning him of Brutus and Cassius. He also names others, stating,
There is but one mind in all these men, and it is bent against Caesar.... Security gives way to conspiracy. The might gods defend thee! (2.3.3-5)
Decius steps forward with a different paper, a "humble suit." This is a petition. Hearing that Decius has a petition, Artemidorus begs Caesar to read his first, contending that his "suit" touches Caesar more closely. Unfortunately, Caesar tells Artemidorus that because the petition is about himself, he will put it last. Then, Publius comes along and pushes Artemidorus aside, and Caesar goes up the stairs and into the Senate House.