Che ci siano incertezze sul numero delle legioni di Pompeo mi sembra chiaro. La fonte principale è Cesare, oltre a Pollione che fu usato da Appiano, entrambi non sono al fianco di Pompeo, naturalmente, ma sul fronte avverso, quindi è ovvio che diano cifre chiarissime per le legioni cesariane e diventino incerti per quelle nemiche. Si saranno basati sulle notizie degli esploratori, dei disertori e dei prigionieri, dopo lo scontro, non è detto che queste persone fossero informate perfettamente su tutto (forse Bruto potrebbe essere stato più al corrente, visto che era nei quadri comando).
Ecco cosa dice Appiano (Le Guerre Civili II) sulle truppe a Farsalo (scusate ma è in inglese, mi secca tradurre):
"70 Since many writers differ as to Caesar's army, I shall follow the most credible Roman authorities, who give the most careful enumeration of the Italian soldiers, as the backbone of the army, but do not make much account of the allied forces or record them exactly, regarding them as mere foreigners and as contributing little to the issue of the day. The army, then, consisted of about 22,000 men and of these about 1000 were cavalry. Pompey had more than double that number, of whom about 7000 were cavalry. Some of the most trustworthy writers say that 70,000 Italian soldiers were engaged in this battle. Others give the smaller number, 60,000. Still others, grossly exaggerating, say 400,000. Of the whole number some say Pompey's forces were half as many again as Caesar's, others that they were two-thirds of the total number engaged. So much doubt is there as to the exact truth. However that may be, each of them placed his chief reliance on his Italian troops. In the way of allied forces Caesar had cavalry from both Cisalpine and Transalpine Gaul, besides some light-armed Greeks, consisting of Dolopians, Acarnanians, and Aetolians. Such were Caesar's allies. Pompey had a great number from all the eastern nations, part horse, part foot. From Greece he had Lacedaemonians marshalled by their own kings, and others from Peloponnesus and Boeotians with them. Athenians marched to his aid also, although proclamation had been made that they, being consecrated to the Thesmophori, should do no harm to the army of either party. Nevertheless, they wished to share in the glory of the war because this was a contest for the Roman leadership.
71 Besides the Greeks almost all the nations of the Levant sent aid to Pompey: Thracians, Hellespontines, Bithynians, Phrygians, Ionians, Lydians, Pamphylians, Pisidians, Paphlagonians; Cilicia, Syria, Phoenicia, the Hebrews, and their neighbours the Arabs; Cyprians, Rhodians, Cretan slingers, and all the other islanders. Kings and princes were there leading their own troops: Deïotarus, the tetrarch of Galatia, and Ariarathes, king of Cappadocia. Taxiles commanded the Armenians from the hither side of the Euphrates; those from the other side were led by Megabates, the lieutenant of King Artapates. Some other small princes took part with Pompey in the action. It was said that sixty ships from Egypt were contributed to him by the sovereigns of that country, Cleopatra and her brother, who was still a boy. But these did not take part in the battle, nor did any other naval force, but they remained idle at Corcyra. Pompey seems to have acted very foolishly in this respect both in disregarding the fleet, in which he excelled so greatly that he could have deprived the enemy of all the supplies brought to them from abroad, and in risking a battle on land with men exulting in their recent labours, and thirsting like tigers for blood. Although he had been on his guard against them at Dyrrachium, a certain spell seems to have come over him, most opportunely for Caesar, with the result that Pompey's army became light-headed to a degree, taking entire charge of its commander, and rushing into action in a most unworkmanlike way".
I morti a fine battaglia: "82 The losses of Italians on each side — for there was no report of the losses of auxiliaries, either because of their multitude or because they were despised — were as follows: in Caesar's army, thirty centurions and 200 legionaries, or, as some authorities have it, 1200; on Pompey's side ten senators, among whom was Lucius Domitius, the same who had been sent to succeed Caesar himself in Gaul, and about forty distinguished knights. Some exaggerating writers put the loss in the remainder of his forces at 25,000, but Asinius Pollio, who was one of Caesar's officers in this battle, records the number of dead Pompeians found as 6000.
Such was the result of the famous battle of Pharsalus".
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"Odiare i mascalzoni è cosa nobile" (Quintiliano)
"Ingiuriare i mascalzoni con la satira è cosa nobile, a ben vedere significa onorare gli onesti" (Aristofane)