The act opens on a plain in Syria. Ventidius, a Roman officer, was sent to fight the Parthians by Antony at the end of Act II, Scene 3. It is not clear how much time has passed, but in this scene, Ventidius has returned to Rome, and he describes his victory over the Parthians to Silius, one of his officers. Ventidius relates how he killed Pacorus, the Parthian king's son in revenge for the death of Marcus Crassus, a noble Roman, killed by the Parthians in another battle in which Crassus's entire force was annihilated. Sillus encourages Ventidius to make the most of his victory by returning home in triumph, but Ventidius refuses, noting that it is better not to appear too successful, lest he shame his commander, Antony, by comparison. He tells about another officer of Antony's, Sossius, who served well in Syria, but fell out of favor; it is implied that his great success as a warrior may have had something to do with it.
Silius praises Ventidius's discretion, and Ventidius says that he will write to tell Antony about the victory, although he will be careful not to boast.
The subject matter of the entirety of Act III is war, and this chapter serves to introduce this facet of the play to the audience while also continuing the theme of the on-going foreign battles, a theme that has been woven into the plot by events in earlier scenes, such as Antony's command to Ventidius in Act II.
This scene focuses primarily on the relationship between war and power. Not only are the rival generals, Caesar and Antony, vying against each other for ultimate power, but the lesser officers are also continually seeking their own advancement. Ventidius is wise here to avoid seeking excessive military glory. He does not want Antony to think he is trying to rival him in military achievements.
The language used by Shakespeare in this brief scene suggests the power, the action, and the cruelty of war. The Parthians, a fierce nation of horsemen, are described as being "darting" Parthians. It has been suggested by several critics that this word was meant to refer to the Parthian practice of turning around to shoot arrows at their enemy while riding away from them. Whatever their military strategy, however, they have been defeated.
Perhaps it should be noted that Shakespeare was paralleling history when he made Ventidius cautious about boasting too much of his success. Ventidius is wary of Antony's thinking that he might perhaps be trying to become "his captain's captain"; a soldier should not be so successful that he overshadows his commander. This concern with ambition and the consequences of seeming too ambitious are understandable when we consider the means used at that time to acquire power. Soldier-emperors like Antony or Caesar would inevitably be suspicious of any officer who might remind them too much of themselves during their earlier careers when they were filled with bravery and unbridled ambition.
Silius praises Ventidius for having that "distinction" (discretion) without which a skilled soldier grants no "distinction" (honor) at all. This play on words suggests the dual qualities which are the key ingredients for the best officers: valor and the discretion to know when to act and when not to.
There is some irony in the contrast between the cautious and soldierly Ventidius and the more impulsive Antony. As we shall see later in this act, Antony actually lacks that very discretion talked about here when he plans his battles. Tragically, it leads to his own destruction.