Appian of Alexandria Civil Wars 4.17.133

[133] When it became necessary for them to take up arms, two whole years had not elapsed ere they had brought together upward of twenty legions of infantry and something like 20,000 cavalry, and 200 ships of war, with corresponding apparatus and a vast amount of money, some of it from willing and some from unwilling contributors. They carried on wars with many peoples and with cities and with men of the adverse faction successfully. They brought under their sway all the nations from Macedonia to the Euphrates. Those whom they had fought against they had brought into alliance with them and had found them most faithful. They had had the services of the independent kings and princes, and in some small measure even of the Parthians, who were enemies of the Romans; but they did not wait for them to come and take part in the decisive battle, lest this barbarous and hostile race should become accustomed to encounters with the Romans. Most extraordinary of all was the fact that the greater part of their army had been the soldiers of Gaius Caesar and wonderfully attached to him, yet they were won over by the very murderers of Caesar and followed them more faithfully against Caesar’s son than they had followed Antony, who was Caesar’s companion in arms and colleague; for not one of them deserted Brutus and Cassius even when they were vanquished, while some of them had abandoned Antony at Brundusium before the war began. The reason for their service, both under Pompey aforetime and now under Brutus and Cassius, was not their own interest, but the cause of democracy; a specious name indeed, but generally hurtful. ¹ Both of the leaders, when they thought they could no longer be useful to their country, alike despised their own lives. In that which related to their cares and labors Cassius gave his attention strictly to war, like a gladiator to his antagonist. Brutus, wherever he might be, wanted to see and hear everything because he was by nature a seeker after knowledge.