Throughout the entire struggle [the civil war] not a single Caesarian deserted, and many of them, when taken prisoners, preferred death to the alternative of serving with the Pompeians. Such was their fortitude in facing starvation and other hardships, both as besiegers and as besieged, that when Pompey was shown at Dyrrhachium the substitute for bread, made of grass, on which they were feeding, he exclaimed: 'I am fighting wild beasts!' Then he ordered the loaf to be hidden at once, not wanting his men to find out how tough and resolute the enemy were, and so lose heart.
That is pretty hard-core, though I suppose Pompey could have used the same loaf of grass bread to demonstrate to his soldiers how close the Caesarians were to defeat. After all, how much longer can an army of men keep fighting with nothing more than grass to sustain them? They would eventually weaken, and as long as the Pompeians had adequate supplies they would be sure to prevail. Eventually.
But Pompey didn't prevail. He lost in the end, and Rome was won by Julius Caesar, to be transformed from a republic into the new Roman Empire, ushering in a new age of complete, dictatorial, tyrannical domination of the world's greatest power at the time.
Well, what did you expect? They were eating grass, for Pete's sake!