This line is from Act IV, Scene I. In this scene, some time after the death of Caesar, the Republic is in turmoil. With Antony, Lepidus, and Octavius in charge--the triumvirate--Antony and Lepidus compile a list of their political enemies and mark ("prick'd") the names of those who must die. Octavius tells Lepidus that his brother must die; Lepidus agrees on the condition that Antony's nephew, Publius, die. Marc Antony agrees. Then, when Lepidus leaves, Antony tells Octavius of his plans to use Lepidus for his political objectives and then cut him off:
Octavius, I have seen more days than you;/And though we lay these honors on this man,/To ease ourselves of divers sland'rous loads [various burdens of blame]/To groan and sweat under the business, Either led or driven, as we point the way;/And having brought our treasure where we will,/Then take we down his load, and turn him off,/(Lide to the empty ass) toshake his ears/And graze in commons [public pastures] (IV,i,18-27)
When Octavius objects, saying that Lepidus is a "tried and valiant soldier" (IV,i,28), Antony coldly retorts, "So is my horse...." (IV,i,29). This remark is much different in tone from Antony's loving words said over Caesar's body in Act III, scene 1.
That power corrupts is evidenced in this scene as the triumvirate move men's lives around as those they are pieces on a chess board. Ironically, the corrupt political power of these men well superpasses the tyranny which Brutus feared from Caesar. And, also ironically, Antony's prediction in Act III that
A curse shall light upon the limbs of men;/Domestic fury and fierce civil strife/Shall cumber all the parts of Italy (III,i,263-265)
is fulfilled by Marc Antony himself!
Shakespeare's Julius Caesar is a staple of high school English classes. It is one of the most accessible Renaissance plays for students to understand.
At this pint in the play, Antony, Octavius and Lepidus have formed an association (a triumvirate) together to get revenge on the men who killed Caesar. Antony has a paper with names on it and he says,
These many, then, shall die; their names are prick'd." (iv.1.1)
The men then mark more names of people who will be executed, including the brother of Lepidus and the son of Marc Antony's sister. Octavius says,
"Prick him down, Antony" (iv.1.4)
concerning Ledipus' brother; his brother will also have to be executed.
Antony replies that,
"He shall not live. Look, with a spot I damn him." (iv.1.7)
It is this scene which precedes the battle between the armies of Brutus and Cassius versus Marc Antony and Octavius. The scene displayed the fact that executions will go on even without Julius Caesar; maybe life really hasn't changed that much for the better for Rome.