Shakespeare introduces Artemidorus, a teacher of rhetoric, in the very brief Scene 3 in Act II. Artemidorus is reading aloud from his own letter which he hopes to be able to give to Caesar as the great man passes by on his way to the Senate. In the letter, Artemidorus warns Caesar to beware of Brutus, Cassius, Casca, Cinna, Trebonius, Metellus Cimber, Decius Brutus, and Caius Ligarius. When Artemidorus finishes reading his warning-letter he speaks the following soliloquy.
Here will I stand till Caesar pass along,
And as a suitor will I give him this.
My heart laments that virtue cannot live
Out of the teeth of emulation.
If thou read this, O Caesar, thou mayest live;
If not, the Fates with traitors do contrive.
In Act III, Scene 1, Artemidorus succeeds in handing his letter to Caesar—but not in getting him to read it. Caesar, with false humility, tells him:
What touches us ourself shall be last served.
Artemidorus continues to urge him to read his letter, knowing that if Caesar waits until he reaches the Capitol it will be too late. Caesar is escorted by some of the very men named in the warning letter. But Artemidorus is an unimportant person who just happens to have important knowledge. One man even calls him "sirrah" as if to emphasize his lowly status.
PUBLIUS To Artemidorus
Sirrah, give place.
This little incident, which Shakespeare borrowed from Plutarch's Life of Caesar, adds to the dramatic tension, as it continues to build up until the conspirators all surround and kill Caesar.