It was an utter impossibility for Shakespeare to represent a major battle on the stage. He was forced to do what he did, which was to suggest that the battle was occurring offstage while being observed by a few characters onstage. Since the major characters--Brutus, Cassius, Antony, and Octavius--were actively engaged in the battle they would be offstage with their troops much of the time. Therefore, Shakespeare would have to make considerable use of minor characters to observe the fighting and to report significant developments to each other. He probably utilized some sound effects offstage, such as clashing swords and shouting, to help sustain the illusion that a big battle was in progress. But there is no actual fighting seen on the stage.

A good example of how Shakespeare simulates fighting offstage is to be seen where Cassius says

Go, Pindarus, get higher on that hill.

My sight was ever thick. Regard Titinius,

And tell me what thou not'st about the field.

There has been no previous indication that Cassius was nearsighted. This is just a way of using dialogue to convey information to the audience about action supposedly taking place offstage. Pindarus is gone and back in moments to report:

Titinius is enclosed round about

With horsemen, that make to him on the spur.

Yet he spurs on. Now they are almost on him.

Now Titiniius. Now some light. O, he lights too.

He's ta'en.

Shakespeare had neither the space nor the resources to try to show a large number of men fighting onstage with swords, shields, spears--and even horses!

The turning point in the key battle in Shakespeare’s The Tragedy of Julius Caesar happens because of a simple mistake by a minor character.

In Act V Cassius is downhearted because his own men have begun to flee the battle. In fact, he has even killed one of them himself for turning and running away. This may predispose him to accept the bad news he is about to get. He sends his friend Titinius to see what the enemy is doing, then asks another minor character, Pindarus to watch and see what happens with Titinius. Pindarus reports this:

Titinius is enclosed round about
With horsemen, that make to him on the spur;
Yet he spurs on. Now they are almost on him.
Now, Titinius! Now some light. O, he lights too.
He's ta'en. And, hark! They shout for joy.

Unfortunately, Pindarus has misconstrued what he has seen. Believing that the enemy has overtaken Titinius, he seals Cassius’ fate by telling him, in effect, that the battle is lost. But the truth is that the men who have met Titinius are Brutus’ victorious troops. Brutus arrives on the scene after Cassius has had Pindarus kill him. Without Cassius, Brutus is doomed.