On War And Warfare

Pompey the Great and the Campaign of 49 B.C.:

Analysis of a Military Blunder


Albert A. Nofi 

The innovative analytic techniques which gave birth to modern wargaming – systems analysis, operations research, simulation modeling – have been extensively applied to the examination of modern – and future – warfare.  They have been less widely applied to the study of earlier conflicts.   Most existing efforts to use such techniques in the study of warfare in the ancient period have been interesting but limited due to their commercial nature.  Attempts to embark upon more serious, scholarly undertakings have not been successful, due partially to a shortage of personnel trained in both the classics and simulation design and partially to a lack of academic interest.  Nevertheless there are innumerable military events in the pre-modern age which lend themselves readily to serious examination using these techniques.  One of the best examples is the campaign between C. Julius Caesar and Gn. Pompeius Magnus in Italy in 49 B.C., for such an analysis rather clearly demonstrates that Pompey the Great committed a  grave strategic blunder.

In 60 B.C. Gaius Julius Caesar, Gnaeus Pompeius Magnus, and M. Licinius Crassus had formed a consortium for the purpose of plundering the state, a cabal known to history as the "First Triumvirate."  They were rather successful in this conspiracy, seizing high office and assigning each other various lucrative provincial commands.  But as time passed, the arrangement began to deteriorate.  Caesar's daughter Julia, who had been given in marriage to the considerably older Pompey, died in 54 B.C.  Crassus met his end on campaign against Parthia in 53 B.C.  By 50 B.C. Pompey had been won over to the party of the establishment, which feared Caesar as a champion of the increasingly restive citizenry.[1]   Tension between the two grew and war soon became more or less inevitable.

At the time, late 50 B.C. by modern reckoning, the Republic appears to have had between 21 and 23 legions under arms.  These were deployed primarily on the fringes of Roman territory.

Legionary Postings, Late 50 B.C.[2]


















Pompey Senatorial












A. Although Pompey was titular commander, in his absence command was being exercised by three legates.
B. Including legions stationed in Gallia Cisalpina, by excluding 22 cohorts of newly recruited manpower not yet organized into legions, some of which would go to form Caesar's famed Alaudae, Gallic-speaking legion.
C. These included Pompey's old 1st, from his consular series raised in 52 B.C., which had been lent to Caesar for the Gallic Campaign of 52-51 B.C., and Caesar's old 15th, which he had raised in 53 B.C. In early 50 B.C. a decree of the Senate had forced Caesar to turned both legions over to Pompey in anticipation of the latter’s planned Parthian Campaign. [3]
D. According to Cicero, two legions were so under strength as to be the equivalent of but one regularly constituted legion. [4]
E. Two of these legions were certainly recruited from the remnants of the six legions lost by Crassus in 54 B.C. The evidence for the other two is less firm.

Matters came to a head very early in 49 B.C., when the Senate effectively declared Caesar an outlaw.[5]   On 11 January 49 B.C. Caesar led his army across the Rubicon, a little river in northeastern Italy which marked the boundary of his provinces.[6]

Caesar’s invasion of Italy presented Pompey with two options:

1. Stay and fight.

2. Flee.

If Pompey chose to stay and fight, he would face an immediate clash of arms with the aggressive Caesar.  However, although he was arguably as good a commander as Caesar was, he had not taken the field for many years.  Moreover, he had only two seasoned legions, both of which had recently been in Caesar's service, and was trying to raise at seven new legions with which to face the invasion. [7]  Caesar was coming south with at least three, probably six, and possibly ten veteran legions, plus at least two legions of recruits.  Moreover, the situation deteriorated very rapidly.  So swift was Caesar’s advance, that four of the seven legions which Pompey was attempting to raise soon fell under Caesar’s control.[8]   In short, the concentration of forces against him was something between 30 and 130 to 35, based on the relative "raw combat power" of the available forces.   This estimate is loosely based on an application of  the late Trevor N. Dupuy’s "Quantified Judgment Method."  Military organization, equipment, and doctrine were identical on both sides, which greatly simplifies such calculations.  Legions in this period generally numbered approximately 4,500 men.  If we assume that a veteran legion has a strength of 10, we can use Caesar’s own estimate that veteran troops were about twice as effective as recruits, to set the value of green legions at 5.[9]

Possible Pompeian Outcomes

A Hypothetical Italian Campaign in 49 B.C.[10]

Worst Case

Probable Case

Best Case

















 In fact, the best case situation was that which actually occurred.  Caesar invaded Italy with his three veteran legions, plus two-legion equivalents of recruits, and supplemented his army with four of the legions Pompey had been trying to raise, giving him a nearly two-to-one edge in manpower over his rival.  These were not particularly good odds.  All other things being equal, Pompey could hope for no more than a drawn battle, and there was a very strong likelihood that he might suffer a disastrous defeat.  In consequence, flight was Pompey’s only practical alternative.  And so he pulled his forces into the port of Brundisum while Caesar overran most of Italy without a fight.

Of course flight had its drawbacks.  In taking flight, Pompey would inevitably suffer a loss of prestige and, worse, the loss of the enormous human and financial resources of Italy.

In terms of manpower, during the first year of the civil war, Caesar would raise about 14 legions in Italy, including the four taken from Pompey.  Between the end of 49 B.C. and his death, in March of 44, Caesar would raise a further 20 or so legions in Italy, for an annual average of four or five legions.  Thus, Caesar would put a minimum of 155,000 men under arms in Italy over five years, out of a citizen population of perhaps 1,150,000 men. [11]

By abandoning Italy Pompey also left Caesar a considerable financial windfall.  Although Italy, only lightly taxed, contributed but 30 million sestertii to annual state revenues, estimated at some 350 million, there was a vast amount of the Republic’s treasure on deposit in Rome, primarily in various temples. [12]   The precise figure cannot be estimated with any degree of accuracy.  In 88 B.C. Sulla had obtained 37.8 million sestertii from the various state treasuries in order to finance his campaign in the Orient.[13]  Despite this, there remained enough left for the younger Marius to make off with an additional 60 million sestertii in 83 B.C.[14]  Caesar appears to have done at least as well.  In the first weeks of his invasion of Italy he raided the state treasuries, making off with enormous sums.   Indeed, so flushed was Caesar's war chest that he returned 6 million sestertii seized from Pompey’s legate Domitius Ahenobarbus at Corfinum in the first weeks of the war.[15]  

Naturally, these enormous resources of men and treasure would have been of great value to Pompey's cause.  Nevertheless, if his cause was to have any hope of prevailing, Pompey had no choice but to flee.   Moreover, he could do in safety, for he had control of the seas.   Within months of the outbreak of the civil war he had managed to concentrate some 600 ships, including at least 300 triremes. [16]  In contrast, the best Caesar was “destitute of ships,” being able to muster only about 150 vessels of various types.[17] Having determined, on the basis of the military situation, that flight was the best course of action, Pompey was now confronted with three possible directions in which to flee.  These were:

                        A). To Africa,

                        B). To Spain,

                        C). To Greece.

The African Option.  Flight to Africa was an attractive possibility.  The province was just a few day's sail from Italy, which would permit him to pose a constant threat to Caesar's base.  In addition, Africa's location could be of great value in developing alternative strategies due to its central position, through the use of his naval supremacy.  Militarily the province also offered several advantages.  Roman – and romanized – manpower resources were considerable, so that Pompey's supporters would activate between eight and ten legions there within two years, albeit that not all were at 4,500 men.[18]

Africa offered yet another advantage, for that Pompey had an ally there in the person of King Juba I of Numidia.  Though not necessarily completely trustworthy, Juba had reorganized his army along Roman lines, and possessed bring four legions plus a sizeable contingent of light troops, a numerous force of cavalry, and many elephants which would be at Pompey's command.[19] 

Finally, Africa had substantial financial resources.  Its annual contribution to the state revenues has been estimated at some 8.6% of the total, about 30 million sestertiii, a tax yield equal to that of Italy itself.[20] 

The Spanish Option.   If Pompey chose to flee to Spain he would also find many advantages.  He was technically proconsul of the Spanish provinces, had campaigned there for several years in the past, and had the favor of the populace, both Roman and native.[21]  From Spain, Pompey would be able to threaten Caesar's recent conquests in Gaul, and possibly fall upon Italy from the Alps, for he had strong allies in the romanized southern portions of Gaul, where the city of Massilia had declared for him against Caesar.[22]

More importantly, there were six seasoned legions in Spain plus many auxiliary troops, all under commanders loyal to Pompey.[23]  In addition, thee was sufficient Roman and Romanized manpower in Spain to eventually permit the raising of about a dozen additional legions over the next few years.[24]

Finally, Spanish financial resources were considerable.  The two provinces normally produced an annual contribution of about 8.0% of the state's revenues, some 28 million sestertii, and were so wealthy they could readily be squeezed for more.[25]

The Greek Option.  Choosing to go eastwards, to Greece, also offered a number of advantages, not least because Greece controlled access to the wealthy provinces of Asia and Syria.   Geographically, Italy was but a day's sail from Greece, so Pompey would be in a good position to threaten Caesar's control of the peninsula.  Politically, Greece and the Orient were familiar territories to Pompey, for he had extensive campaigning experience there, and was quite popular in some quarters. [26]

There were some military resources in these areas, with two seasoned, albeit under strength, legions in Cilicia, and four more in Syria.[27]  However, the pool of additional manpower was poor.  By concentrating all available forces, scraping the bottom of the barrel for Roman and Romanized manpower, by calling up discharged veterans, and by enrolling legally unqualified personnel, the best that could be done by early 48 B.C. was to effect a net gain of two new legions, bring the existing ones up to full strength, and concentrate a substantial force of cavalry and light infantry, leaving Pompey with just eleven legions. [28]

But if the Eastern provinces were poor in manpower, they were immensely wealthy in treasure..   Taken together, they generated about 51.4% of state revenues, some 180 million sestertii.[29]  So Pompey would not want for money.

Thus, each of the choices open to Pompey had particular advantages.  A comparison of the differences among these may be useful at this point.

Comparison of Strategic Consequences .   Strategically, each of Pompey’s three options offered certain advantages and disadvantages.

Strategically, Africa was probably the optimal choice.  From Africa, Pompey would not only be able to pose a direct threat to Italy by sea, but also would be able to shift forces easily in any direction to counter any possible move by Caesar or for his own purposes.  He would, of have to pay the political price of relying heavily on a non-Roman ally, but once Caesar had been taken care of Pompey would be able to cope with Juba of Numidia at his leisure.

Greece put Pompey in a position to pose the most direct and immediate threat to Caesar's base in Italy.  But he would be poorly placed to counter Caesar's activities in the West; Should Caesar strike at Spain or Africa, Pompey would find it difficult to respond from Greece, save by direct attack on Italy. 

From Spain, Pompey would be less able to threaten Italy directly, and unable to intervene quickly in Greece or even Africa, but  would be in an excellent position to threaten Gaul, and thence advance overland into Italy.  Moreover, given Pompey's naval supremacy, Spain could still be useful for operations oversea against Italy.

Comparison of Operational Consequences .  There exist significant differences in the operational military consequences of each of the options.  These may best be examined in the form of a tabular presentation.

Probable Outcomes

Projected Alternative Military Situations

49-48 B.C.



P:C Ratios

Potential Outcomes









































Leg is the number of legions which would have been available in the theater assuming a decision was reached din 48, as was the case in Greece, including the five which Pompey would have brought with him from Italy and those which Caesar would have had available.
C.P. is the estimated combat power of these legions, assuming veteran ones at 10, recruit ones at 5, and Numidian ones at 7.
P:C Ratio is the balance of forces between Pompey and Caesar, in both legions and combat power.
Outcomes are based on the Imperium Romanum II combat results system.

By taking refuge in Spain, Pompey would have enjoyed an immediate, and perhaps decisive military advantage.  Africa would likewise offer important military advantages. However, the military consequences of a retirement to the Eastern provinces, would be clearly unfavorable, particularly since Caesar would be able to concentrate the bulk of his veteran forces in that theater.

Consequences Financial of Comparison.   Regardless of the theater to which Pompey chose to retire to order to rebuild his fortunes, his financial situation would not have changed significantly, since he would retain political control of the other areas.  Similarly, Caesar would retain control of various areas as well.  Thus, the fiscal strength of each side would remain essentially unchanged whichever option Pompey chose.

The provinces which were controlled by Pompey, Macedonia, Greece, Crete, Asia, Bithynia, Pontus, Cilicia, Cyprus, Syria, Cyrenaica, Africa, and the Spain's, yielded the bulk of the Republic’s tax revenues, some 238 million sestertii, about 68% of annual state income. In contrast, Gaul, Cisalpina, and Italy itself, plus Sicily, Sardinia, and Corsica, controlled by Caesar, yielded revenues of 112 million sestertii, only about 32% of annual state income.

To be sure there would be some difficulty in transferring funds from theater to theater, but Pompey's control of the seas was undisputed. So financially resources, Pompey was comfortably well off regardless of which theater he chose to retire to. Indeed, arguably, had he chosen to take refuge in Spain or Africa, he might readily have used his fleet to interfere with Caesar’s ability to gain financial benefit from Sardinia, Corsica, and Sicily, 30 million sestertii annually. As the costs of operating an army were enormous, such a blow would Caesar a lot more than it would have helped Pompey.[30]

Operating a single 4,500-man legion for a year ran to some 4 million sestertii.[31]  Thus, the revenues of the provinces which Pompey controlled would have been sufficient to maintain under arms nearly 60 legions, a number which would have pressed the limits of the manpower resources of the Roman state.[32]  In fact, Pompey's faction never mustered more than 23 legions at any one time, peak strength being reached during the early months of 48 B.C.  As a result, his enormous revenues were more than sufficient to his needs.  On the other hand, Caesar's ordinary revenues were rather tight, being sufficient to maintain only 28 legions on active service.  From 49 B.C. through 46 B.C. Caesar actually averaged about 29 legions under arms at any given time, though his peak strength gradually rose to 36.  To be sure, in this same period he added considerably to his revenues, by acquiring control of the Spain's and the Orient from the Senatorial party, as well as through confiscations.  But his expenditures were enormous as well.  At the onset of the civil war he had promised a rather lavish donative to his troops, amounting to about 102.9 million sestertii per legion, thereby incurring an obligation to pay over 3.7 billion sestertii at the end of the civil war, a sum equal to about 1060% of the total annual state revenues. [33] 

Conclusion .  Given its strategic and military advantages, Spain was Pompey's optimal objective upon retiring from Italy in early 49 B.C.   Failing Spain, Africa offered significant advantages.  The least desirable area to which he could withdraw was Greece and the Oriental provinces, for, while enormously wealthy, they offered little in the way of military resources.   In the event, Pompey chose precisely the worst option.  On 17 March 49 B.C., Pompey took ship for Macedonia. [34] 

The consequences were fatal to his cause.

Pompey's decision in this instance has not hitherto been questioned.  Lawrence Keppie calls the retirement "sensible on strategic grounds,” while Robin Seager states flatly that "[Pompey] intended to use the resources of the East to blockade and if need be to reconquer Italy,” and F.E. Adcock goes so far as to say, ". . . Pompey adopted the course which gave the most chances."[35]   Even Hans Delbruck, the inventor of modern military analysis, overlooked Pompey's poor judgment in this matter, for he merely made some general remarks about the hopelessness of the situation in Italy, concluding with an almost casual mention that Pompey retired to Greece, before hurrying on to an analysis of Caesar's Spanish Campaign.[36]

 Nevertheless, it is difficult to escape the conclusion that Pompey made a serious error of judgment.  Indeed, Caesar himself is reported to have been "astonished" by Pompey's decision.[37]   He clearly understood the implications of Pompey's actions.  Resisting the temptation to pursue his foe immediately, Caesar set out instead for Spain, saying "I am off to meet an army without a general; when I return, I shall meet a general without an army."[38]

Which is precisely what he did.


[1] The causes of the bout of civil disorders and wars which plagued the Roman Republic in its last century have been rehearsed many times, usually in terms of modern socio-political notions – such as Marxism – which lack validity when applied to a near-subsistence society over 2,000 years in the past.  Put most simply, it came down to a failure on the part of the Roman elite to adequately understand that the existing political and military institutions of the state were leading to the disenfranchisement and impoverishment of the yeoman peasantry, on which the strength of the state lay.  On this, see  P.A. Brunt, Italian Manpower, 225 B.C.-A.D. 14 (Oxford: 1971), passim.

 [2] Compiled from Caesar, B.C, i, 38; iii, 4; Caesar, B.G., viii, 46, 54; Cicero, ad Fam., XV, 4, 3.

 [3] Caesar, B.G., viii, 54, and B.C., i, 9.

 [4] Cicero, ad Fam., XV, 4, 3

 [5] For a fairly even handed contemporary summary of the events immediately preceding the crossing of the Rubicon see Suetonius, Div. Iul., 29-32

 [6] The peculiarities of the Roman calendar were such that the date was out of synchronization with the seasons by about ten weeks.  As a result although 11 January was the legal date, it was actually about 19 October of 50 B.C.  In 46 B.C. Caesar would institute a calendar reform which set matters aright, but resulted in that year having fifteen months.

 [7] Caesar, B.G., vii, 54, and B.C., i, 9; Appian, B.C.,  II, viii, 49. 

 [8] Pompey had actually raised about seven legions of recruits, but so rapid was Caesar's advance that four of these fell under the latter's control; Cf.,  Caesar, B.G., i, 25; Plutarch, Cae, xxxv, 1, and Pomp., lx, 4; Velleius, II, xl, 1.

[9] Caesar, B.C., III, 28.4.

[10] The probable outcomes shown in the table are based on the standard combat results table used in this writer’s Imperium Romanum II (New York: 1989), which was derived from an analysis of the outcomes of several dozen battles.  It is assumed that, having the stronger forces, Caesar was most likely to do the attacking, which was quite normal for him in any case. 

[11] These figures assume legions at 4,500 men each, generally regarded as the norm for the period, and exclude men serving afloat and as auxiliaries.  For population figures see Livy, xlviii & xcvii, recording the census of 70-69 B.C., as modified by the calculations in Brunt, pp. 90-99, who makes the reasonable assumption that about 150,000 of the 1,150,000 adult male citizens were abroad.  Note that the legionary manpower raised by Caesar in Italy was some 20% greater than that which Pompey had senatorial authorization to levy at the onset of the civil war, as noted in Appian, B.C., II, 34.  The total number of legionaries raised in Italy during 49-44 B.C. amounted to  perhaps as many as 175,000 men, including the three recruit legions which remained with Pompey.  Considering the number of men raised for the fleet and to serve as officers with auxiliaries, the total number recruited in the period must have been at least 200,000.  Add to this figure the 80,000 already under arms at the end of 50 B.C. and the manpower drain of this bout of civil wars amounted to 280,000 men, or about 24.4% of total male citizenry;  Cf., Brunt, p. 511.

[12] This calculation is based on Plutarch, Pomp., 45, and Tenney Frank, An Economic History of Rome (Baltimore: 1920), pp. 136ff.

[13] Appian, B.M., 22.  If one thinks of sestertii as dollars, and adds a zero, some notion of the magnitude of the sums involved will become clear.

[14] Valerius Maximus, 7, 6.4; Pliny, Hist. Nat., 33, 16.

[15] Caesar, B.C., i, 23.

[16] Appian, B.C., II, 49 & 87; Caesar, B.C., iii, 3, 5 & 3, 27; Cicero, ad Att., IX, 9, 2; and Plutarch, Pomp., lxiv, 2, which gives him but 500 warships. 

[17] Plutarch, Cae, xxxv, 3; Appian, B.C., II, 41 & 49: Caesar, B.C., i, 36, 5.

[18] Appian, B.C., II, xiv, 96; Caesar, B. Afr., 1; Caesar, B. Alex., xxxiv, 5; Caesar, B.C., ii, 23.

[19] Caesar, B. Alex., xxxiv, 5.

[20] Plutarch, Pomp., 45.

[21] Plutarch, Pomp., xviii-xxi; Plutarch, Sert., xviiiff; Caesar, B.C., 29.

[22] Caesar, B.C., i, 34-36, & ii, 1-22; Florus, II, xiii, 23; Velleius, II, xl, 3.  The Massiliots, clients of the Domitii Ahenobarbi, solidly Pompeian supporters, were ultimately besieged by three of the legions Caesar had co-opted from Pompey in the first weeks of the war.

[23] .Caesar, B.C., i, 38.  There was also one legion composed of locally recruited non-Romanized personnel.

[24] Caesar, B.H., 7; Cicero, ad Att., v, 18.2.  One of these legions was eventually recruited from non-Romanized personnel, bringing the total of “vernacular” legions in Spain to two.

[25] .Plutarch, Pomp., 45.

[26] The most extensive ancient account of Pompey's activities in the Orient may be found in Appian's B.M., which may be supplemented by Plutarch's Pomp., xxx-xlii; Velleius, II, xxxiii, 1-4, xxxvii, 1-5, & xl, 1-3.  For a modern synthesis, see Robin Seager, Pompey (Oxford: 1979), pp. 28-55.

[27] Plutarch, Cic., 36; Cicero, ad Fam., XV, 4, 3; Caesar, B.C., iii, 4. 

[28] .Caesar, B.C., iii, 4 & 88.  Most importantly, and see Hans Delbruck,  History of the Art of War within the Framework of Political History, Vol. I, Antiquity (Westport, Ct: 1975), pp 542-555, for a critical examination of Caesar's tally of Pompey’s manpower, with particular concern for the actual numbers involved.

[29] Estimate   based Plutarch Pomp., 45, and Frank, pp. 136ff.

[30] Note that these figures exclude monies derived from plunder, expropriation, loans, and extraordinary levies.  The sums involved could be enormous.  In 49 B.C., Pompey's legate Varro secured 28 million sestertii by an extraordinary levy on Roman citizens resident in Spain, about equal to the annual provincial contribution to the treasury (Caesar, B.C., ii, 18).  In 43-42 B.C., Cassius secured 32.5 million sestertii when he captured Rhodes (Appian, B.C., IV, 73; Dio Cassius, 47, 33.4; Plutarch, Brut., 37) and a further 37.5 million from Tarsus (Appian, B.C., IV, 64; Dio Cassius, 47, 26.2 & 31.3).  Even a minor campaign against some insignificant insurgent hill tribes could yield considerable boodle, such as the 12.5 million sestertii which Cicero captured while governor of Cilicia in 51 B.C. (Cicero, ad. Att., V, 20, 5), a sum greater than the annual provincial revenues. 

[31] Cicero, in Pis., 86; Plutarch, Cae., 28 & Pomp., 55.   Supporting this is Cicero's comment that the two under strength legions he controlled in Cilicia in 51 B.C. each cost about 3 million sestertii in pay and maintenance a year (Cicero, ad Fam., V , 20, 9, & ad Att., V, 11, 5), which was about 60% of the annual revenues of the province (Cf., Frank, pp. 136ff).

[32] .Brunt, pp. 473ff.

[33] This would today easily be in excess of 37 billion dollars. Appian, B.C., II, 102; Dio Cassius, 43,21; Seutonius, Div. Iul., 26, 3.   Note that these figures include only monies promised to ordinary soldiers (20,000 sestertii each), centurions (40,000), and military tribunes (80,000).  Benefits to higher ranking personnel were on a similarly generous scale.   Of course Caesar did not seem to have worried overmuch about money, for if he should lose he would be dead, while if he won he would have the whole empire to plunder.

[34] Cicero, ad Att., IX, 15.6.  In terms of the Julian calendar this was actually 23 December, 50 B.C.

[35] Lawrence Keppie, The Making of the Roman Imperial Army (Totowa, N.J.: 1984),   pp., 104-105; Seager, p. 175; F.E. Adcock, "The Civil War," The Cambridge Ancient History, The Last Age of the Roman Republic,  (Cambridge: 1966), p. 645.

[36] Delbruck, I, 515-516.

[37] Plutarch, Pomp., lxiii, 1.

[38] Suetonius, Div. Iul, 34.

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