In the winter of 48/47, Julius Caesar crossed to Greece, where he wanted to fight against his rival Pompey. However, Pompey was able to block Caesar at Dyrrhachium (modern Dürres). In March, Caesar's colonel Marc Antony managed to reinforce him with four new legions, and on 7 July, the Caesarians were able to move away from the beach, an advance that resembled a flight. The story of the events after the breakout is told by several authors (including Caesar himself); here you can read the account in the Roman History (41.52-63) by Cassius Dio (164-c.235).
The translation was made by Earnest Cary.
[41.52] Pompey did not pursue Caesar, for he had withdrawn suddenly by night and had hastily crossed the Genusus river; however, he was of the opinion that he had brought the war to an end. Consequently he assumed the title of Imperator, though he uttered no boastful words about it and did not even wind laurel about his fasces, disliking to show such exultation over the downfall of citizens. From this same motive he neither sailed to Italy himself nor sent any others there, though he might easily have taken possession of it all. For with his fleet he was far superior, as he had 500 swift ships and could land at all points at the same time; moreover, the sentiment of that country was not opposed to him in any case, and, even if it had been ever so hostile, the people were no match for him in war. But he wished to be far from giving the impression that Italy was the stake for which he was fighting, and did not think he ought to cause any fear to the people who were then in Rome. Hence he made no attempt on Italy, nor even sent to the government any dispatch about his successes; but after this he set out against Caesar and came into Thessaly.
[41.53] As they lay opposite each other the appearance of the camps bore, indeed, some semblance of war, but their arms were idle as in time of peace. As they considered the greatness of the danger and foresaw the obscurity and uncertainty of the issue, and still felt some regard for their common ancestry and their kinship, they continued to delay. Meanwhile they exchanged propositions [...] and appeared to some likely even to effect an empty reconciliation. The reason was that they were both reaching out after the supreme power and were influenced greatly by native ambition and greatly also by acquired rivalry, since men can least endure to be outdone by their equals and intimates; hence they were not willing to make any concessions to each other, since each felt that he might win, nor could they feel confident, if they did reach some agreement, that they would not be always striving to gain the upper hand and would not fall to quarreling again over the supreme issue.
[41.54] In temper they differed from each other to this extent, that Pompey desired to be second to no man and Caesar to be first of all, and the former was anxious to be honored by a willing people and to preside over and be loved by men who fully consent, whereas the latter cared not at all if he ruled over even an unwilling people, issued orders to men who hated him, and bestowed the honors with his own hand upon himself. The deeds, however, through which they hoped to accomplish all that they wished, were perforce common to both alike. For it was impossible for any one successfully to gain these ends without fighting against his countrymen, leading foreigners against kindred, obtaining vast sums by unjust pillage, and killing unlawfully many of his dearest associates. Hence, even though they differed in their desires, yet in their acts, by which they hoped to realize those desires, they were alike. Consequently they would not yield to each other on any point, in spite of the many claims they put forward, and finally came to blows.
[41.55] The struggle proved a mighty one and unparalleled by any other. In the first place, the leaders themselves had the name of being the most skilled in all matters of warfare and clearly the most distinguished not only of the Romans but also of all other men then living. They had been trained in arms from boyhood, had constantly been occupied with them, had performed deeds worthy of note, had been conspicuous for great valor and also for great fortune, and were therefore most worthy of commanding and most worthy of victory. As to their forces, Caesar had the largest and the most genuinely Roman portion of the state legions and the most warlike men from the rest of Italy, from Hispania, and the whole of Gaul and the islands that he had conquered; Pompey had brought along many from the senatorial and the equestrian order and from the regularly enrolled troops, and had gathered vast numbers from the subject and allied peoples and kings. With the exception of Pharnaces and Orodes (for he tried to win over even the latter, although an enemy since the time he had killed the Crassinote[Orodes was king of Parthia. In 53, his general Surena had destroyed the army of the Roman commander Crassus and his son. Pharnaces was the son of Mithridates, the king of Pontus who had been defeated by Pompey. Immediately after the battle of Pharsalus, Pharnaces tried to recover the kingdom of his father. Caesar defeated him in 47 in the battle of Zela ("I came, I saw, I conquered).]), all the rest who had ever been befriended at all by Pompey gave him money and either sent or brought auxiliaries. Indeed, the Parthian had promised to be his ally if he should receive Syria; but as he did not get it, he lent him no help. While Pompey, then, greatly excelled in numbers, Caesar's followers were their equals in strength; and so, the advantages being even, they were an equal match for each other and the risks they incurred were equal.
[41.56] As a result of these circumstances and of the very cause and purpose of the war a most notable struggle took place. For the city of Rome and its entire empire, even then great and mighty, lay before them as the prize, since it was clear to all that it would be the slave of him who then conquered. When they reflected on this fact and furthermore thought of their former deeds [...] they were wrought up to the highest pitch of excitement, believing that those conquests, too, were at stake, and each being eager to acquire the other's glory. For the renown of the vanquished, far more than his other possessions, becomes the property of the victor, since, the greater and more powerful the antagonist that a man overthrows, the greater is the height to which he himself is raised.
[41.57] Therefore they delivered to their soldiers also many exhortations, but very much alike on both sides, saying all that is fitting to be said on such an occasion with reference both to the immediate results of the struggle and to the subsequent results. As they both came from the same state and were talking about the same matters and called each other tyrants and themselves liberators from tyranny of the men they addressed, they had nothing different to say on either side, but stated that it would be the lot of one side to die, of the other to be saved, of the one side to be captives, of the other to enjoy the master's lot, to possess everything or to be deprived of everything, to suffer or to inflict a most terrible fate. After addressing some such exhortations to the citizens and furthermore trying to inspire the subject and allied contingents with hopes of a better lot and fears of a worse, they hurled at each other kinsmen, sharers of the same tent, of the same table, of the same libations. Yet why should any one, then, lament the fate of the others involved, when those very leaders, who were all these things to each other, and had, moreover, shared many secret plans and many exploits of like character, who had once been joined by domestic ties and had loved the same child, one as a father, the other as grandfather,note[Caesar had married his daughter Julia to Pompey; she had died when giving birth to a daughter (more).] nevertheless fought? All the ties with which nature, by mingling their blood, had bound them together, they now, led by their insatiable lust of power, hastened to break, tear, and rend asunder. Because of them Rome was being compelled to fight both in her own defense and against herself, so that even if victorious she would be vanquished.
[41.58] Such was the struggle in which they joined; yet they did not immediately come to close quarters. Sprung from the same country and from the same hearth, with almost identical weapons and similar formation, each side shrank from beginning the battle, and shrank from slaying any one. So there was great silence and dejection on both sides; no one went forward or moved at all, but with heads bowed they stood motionless, as if devoid of life.
Caesar and Pompey, therefore, fearing that if they remained quiet any longer their animosity might become lessened or they might even become reconciled, hurriedly commanded the trumpeters to give the signal and the men to raise the war cry in unison. Both orders were obeyed, but the combatants were so far from being imbued with courage, the at the sound of the trumpeters' call, uttering the same notes, and at their own shout, raised in the same language, they showed their sense of relationship and betrayed their kinship more than ever, and so fell to weeping and lamenting.
But after a long time, when the allied troops began the battle, the rest also joined in, fairly beside themselves at what they were doing.
[41.59] Those who fought at long range were less sensible of the horrors, as they shot their arrows, hurled their javelins, discharged their slings without knowing whom they hit; but the heavy-armed troops and the cavalry had a very hard time of it, as they were close to each other and could even talk a little back and forth; at one and the same moment they would recognize those who confront them and would wound them, would call them by name and would slaughter them, would recall the towns they had come from and would despoil them.
Such were the deeds both done and suffered by the Romans and by the others from Italy who were with them on the campaign, wherever they met each other. Many sent messages home through their very slayers. But the subject force fought both zealously and relentlessly, showing great zeal, as once to win their own freedom, so now to secure the slavery of the Romans; they wanted, since they were reduced to inferiority to them in all things, to have them as fellow-slaves.
[41.60] Thus it was a very great battle and full of diverse incidents, partly for the reasons mentioned and partly on account of the numbers and the variety of the armaments. There were vast bodies of heavy-armed soldiers, vast bodies of cavalry, in another group archers and still others that were slingers, so that they occupied the whole plain, and scattered over it, they fought often with each other, since they belonged to the same arms, but often with men of the other arms indiscriminately.
The Pompeians surpassed in cavalry and archers; hence they would surround troops at a distance, employ sudden assaults, and retire after throwing their opponents into confusion; then they would attack them again and again, turning now to this side and now to that. The Caesarians, therefore, were on their guard against this, and by wheeling round always managed to face their assailants, and when they came to close quarters with them, would seize hold of both men and horses in the eagerness of the struggle; for light-armed cavalry had been drawn up with their cavalry for this very purpose. And all this took place, as I said, not in one spot, but in many places at once, scattered all about, so that with some contending at a distance and others fighting at close quarters, this body smiting its opponents and that group being struck, one detachment fleeing and another pursuing, many infantry battles and many cavalry battles as well were to be seen.
Meanwhile many incredible things were taking place. One man after routing another would himself be turned to flight, and another who had avoided an opponent would in turn attack him. One soldier who had struck another would be wounded himself, and a second, who had fallen, would kill the enemy who stood over him. Many died without being wounded, and many when half dead kept on slaying. Some were glad and sang paeans, while the others were distressed and uttered lamentations, so that all places were filled with shouts and groans. The majority were thrown into confusion by this fact, for what was said was unintelligible to them, because of the confusion of nations and languages, and alarmed them greatly, and those who could understand one another suffered a calamity many times worse; for in addition to their own misfortunes they could hear and at the same time see those of their neighbors.
[41.61] At last, after they had carried on an evenly-balanced struggle for a very long time and many on both sides alike had fallen or been wounded, Pompey, since the larger part of his army was Asiatic and untrained, was defeated, even as had been made clear to him before the action. For thunderbolts had fallen upon his camp, a fire had appeared in the air over Caesar's camp and had then fallen upon his own, bees had swarmed about his military standards, and many of the victims after being led up close to the very altar had run away.
And so far did the effects of that contest extend to the rest of mankind that on the very day of the at least collisions of armies and the clash of arms occurred in many places. In Pergamon a noise of drums and cymbals rose from the temple of Dionysus and spread throughout the city; in Tralles a palm tree grew up in the temple of Victory and the goddess herself turned about toward an image of Caesar that stood beside her; in Syria two young men announced the result of the battle and vanished;note[The two young men can be identified with Castor and Pollux, the divine twins who were sometimes said to have delivered reports of important battles.] and in Patavium, which now belongs to Italy but was then still a part of Gaul, some birds not only brought news of it but even acted it out to some extent, for one Gaius Cornelius drew from their actions accurate information of all that had taken place, and narrated it to the bystanders.note[The same story is told by Plutarch of Chaeronea, Life of Caesar 47. He makes is clear that the incident was witnessed by Titus Livy (59 BCE - 17 CE), who was to become the author of the authorized version of the history of the Roman republic.] These several things happened on that very same day and though they were, not unnaturally, distrusted at the time, yet when news of the actual facts was brought, they were marveled at.
[41.62] Of Pompey's followers who were not destroyed on the spot some fled whithersoever they could, and others who were captured later on. Those of them who were soldiers of the line, Caesar enrolled in his own legions, exhibiting no resentment. Of the senators and knights, however, he put to death all whom he had previously captured and spared, except some whom his friends begged off; for he allowed each friend on this occasion to save one man. The rest who had then for the first time fought against him he released. [...]
This same attitude he adopted toward the princes and the peoples who had assisted Pompey. He pardoned them all, bearing in mind that he himself was acquainted with none or almost none of them, whereas from his rival they had previously obtained many favors. Indeed, he praised these far more than he did those who, after receiving favors from Pompey, had deserted him in the midst of dangers; the former he could reasonably expect would be favorably disposed to him also, but as to the latter, no matter how anxious they seemed to be to please him in anything, he believed that, inasmuch as they had betrayed their friend in this crisis they would, on occasion, not spare him either.
[41.63] A proof of his feeling is that he spared Sadalus the Thracian and Deiotarus the Galatian,note[Deiotarus (c.105-40) was the leader of the Tolistobogii, a Celtic tribe living in what is now central Turkey. He was a loyal ally of Rome during the war against Mithradates of Pontus. In 63/62, Pompey made him king of all Celts in Turkey, which are usually called Galatians. With the help of Roman advisers, he built a large army, consisting of 12,000 infantry and 2,000 cavalry. After his death, these troops were integrated in the Roman army as the legion XXII Deiotariana.] who had been in the battle, and Tarcondimotus, who was ruler of a portion of Cilicia and had been of the greatest assistance to Pompey in the matter of ships. But what need is there to enumerate the rest who had sent auxiliaries, to whom also he granted pardon, merely exacting money from them? He did nothing else to them and took from them nothing else, though many had received numerous large gifts from Pompey, some long ago and some just at that time. He did give a certain portion of Armenia that had belonged to Deiotarus, to Ariobarzanes, king of Cappadocia, yet in this he did not injure Deiotarus at all, but rather conferred an additional favor upon him. For he did not curtail his territory, but after occupying all of Armenia previously occupied by Pharnaces, he bestowed one part of it upon Ariobarzanes and another part upon Deiotarus. These men, then, he treated in this wise. Pharnaces, on his side, made a plea that he had not assisted Pompey and therefore, in view of his behavior, deserved to obtain pardon; but Caesar showed him no consideration, and furthermore reproached him for this very thing, that he had proved himself base and impious toward his benefactor. Such humanity and uprightness did he show throughout to all those who had fought against him.
At any rate, all the letters that were found filed away in Pompey's chests which convicted any persons of good-will toward the latter or ill-will toward himself he neither read nor had copied, but burned them immediately, in order not to be forced by what was in them to take several measures; and for this reason, if no other, one ought to hate the men who plotted against him. I make this statement with a particular purpose, since Marcus [Junius] Brutus Caepio, who afterwards killed him, was not only captured by him but also spared.