I've never read Appian before and could easily have confused him with Arrian,. This source calls Appian "one of the most underestimated of all Greek historian," and his account of the Battle of Philippi, which left Octavian and Antony victorious and led to the demise of Brutus and Cassius, is dense with plausible incident. The conflict began with Brutus and Cassius in far the stronger position. Brutus attacked and broke Octavian's line. But Antony drove back Cassius. Appian elaborates, in the Loeb translation by Horace White:
Some twenty days pass. Brutus, believing tht his adversaries will run short of provisions, undertakes to wait them out. But the adversaries provoke a fight. Brutus tries to hold his force in defense but his soldiers, impatient and hot for blood, erupt into an attack. At first they seem to prevail, but then instead of consolidating their victory, they fall to pillaging Octavian's camp. Again Appian:113 When Cassius was driven out of his fortifications and no longer had even a camp to go to, he hurried up the hill to Philippi and took a survey of the situation. As he could not see accurately on account of the dust, nor could he see everything, but only that his own camp was captured, he ordered Pindarus, his shield-bearer, to fall upon him and kill him. While Pindarus still delayed a messenger ran up and said that Brutus had been victorious on the other wing, and was ravaging the enemy's camp. Cassius merely answered, "Tell him that I pray his victory may be complete." Then, turning to Pindarus, he said, "What are you waiting for? Why do you not deliver me from my shame?" Then, as he presented his throat, Pindarus slew him. This is one account of the death of Cassius. Others say that as some horsemen were approaching, bringing the good news from Brutus, he took them for enemies and sent Titinius to find out exactly; that the horsemen pressed around Titinius joyfully as a friend of Cassius, and at the same time uttered loud hurrahs; that Cassius, thinking that Titinius had fallen into the hands of enemies, said, "Have I waited to see my friend torn from me?" and that he withdrew to a tent with Pindarus, and Pindarus was never seen afterward. For this reason some persons think that he killed Cassius without orders.Thus Cassius ended his life on his birthday, on which, as it happened, the battle was fought, and Titinius killed himself because he had been too late;
114 and Brutus wept over the dead body of Cassius and called him the last of the Romans, meaning that his equal in virtue would never exist again.
The next day Brutus followed the example of his companion and himself fell upon his sword. Shakespeare (deploying an English translation of a French translation of Plutarch's Greek), in the play Julius Caesar compresses it all into two days, and into single act. In the play, Caesar's ghost pays a call on Brutus "to tell thee thou shlt see me at Philippi." "Why," responds Brutus, "I will see thee at Philippi then."128 The day was consumed in preparations till the ninth hour, when two eagles fell upon each other and fought in the space between the armies, amid the profoundest silence. When the one on the side of Brutus took flight his enemies raised a great shout and battle was joined. The onset was superb and terrible. They had little need of arrows, stones, or javelins, which are customary in war, for they did not resort to the usual manoeuvres and tactics of battles, but, coming to close combat with naked swords, they slew and were slain, seeking to break each other's ranks. On the one side it was a fight for self-preservation rather than victory: on the other for victory and for the satisfaction of the general who had been forced to fight against his will. The slaughter and the groans were terrible. The bodies of the fallen were carried back and others stepped into their places from the reserves. The generals flew hither and thither overlooking everything, exciting the men by their ardour, exhorting the toilers to toil on, and relieving those who were exhausted so that there was always fresh courage at the front.Finally, the soldiers of Octavian, either from fear of famine, or by the good fortune of Octavian himself (for certainly the soldiers of Brutus were not blameworthy), pushed back the enemy's line as though they were turning round a very heavy machine. The latter were driven back step by step, slowly at first and without loss of courage. Presently their ranks broke and they retreated more rapidly, and then the second and third ranks in the rear retreated with them, all mingled together in disorder, crowded by each other and by the enemy, who pressed upon them without ceasing until it became plainly a flight. The soldiers of Octavian, then especially mindful of the order they had received, seized the gates of the enemy's fortification at great risk to themselves because they were exposed to missiles from above and in front, but they prevented a great many of the enemy from gaining entrance. These fled, some to the sea, and some through the river Zygactes to the mountains.