Great question!

The Ptolemaic army did undergo some changes between the late 4th and mid-1st Centuries BCE, but the basic shape of the army remained quite consistent across time. Generally speaking, the Ptolemids were not very interested in reforming their army when it was already effective, and the types of soldiers raised did not change much.

However, the strength of the Ptolemaic army was not consistent, and the professional cleruchic soldiers of 1st Century BCE Ptolemaic Egypt (a. were not around or (b. not as numerous or important as they had been in earlier generations. By the 1st Century BCE, the Ptolemaic army included large foreign contingents including Roman legions and mercenaries.

Unfortunately, Ptolemaic records from the 1st Century BCE are notoriously fragmented, it is actually the most poorly documented period of Ptolemaic Egyptian history. A lot of this has to do with the general unrest which defined this period, and led to the destruction and loss of records. This same unrest was part of broader social, economic, and political shifts which impacted the Ptolemaic military.

#The early Ptolemaic Army

To begin with, the Ptolemaic dynasty established a landed class of professional soldiers, the kleroi who mostly emigrated to Egypt between the 4th and 2nd Centuries BCE. These cleruchs filled many different roles in the Ptolemaic army, with cavalry being near the top of the hierarchy and the most affluent, and other infantry being less well paid according to their station. The majority of these were immigrants from Greece and Macedon, although cleruchs are also known to have come from regions like Thrace, Illyria, Syria, Judea, Cyrene, and Egypt.

Graeco-Roman accounts and Egyptian evidence indicates that Ptolemaic infantry were, unsurprisingly, more or less the same as Alexander’s army in terms of the equipment carried and the kinds of troops fielded. The phalanx was the core of the army, and we know that Ptolemids employed Macedonian-style hoplites, peltasts, and light infantry who were equipped with oval shields. But there was a lot of diversity in terms of the equipment wielded by these types of troops, and we also have to take into account the presence of missile-troops. Artistic representations of Ptolemaic and other Hellenistic armies reveal a range of armour types, and a somewhat more consistent range of weaponry.

Around 10% of the Ptolemaic army was cavalry, which was organised and equipped in a similar fashion to the cavalry which Alexander fielded. Papyrological evidence and archives from Egypt tell us a lot about the organisation of the cavalry, and some things about its equipment. The cavalry was divided into hipparchies of 400-500 men, and these hipparchies were further divided into smaller units of horses. Cavalry were equipped with a thorax, a cuirass-belt, a helmet, and a curved sabre rather than a double edged sword, a Macedonian lance, along with the necessary horse equipment which I will not bore you with. So all in all, very similar to 4th Century BCE Macedonian cavalry. However, the Ptolemids did adopt a few unique innovations. For example, Ptolemy II fielded cavalry which was equipped with quilted armour in the Nubian style, and like many Hellenistic armies the Ptolemids fielded unarmoured light cavalry.

Mercenaries also played an important role in the Ptolemaic army, and were a significant royal expense in times of war. Ptolemy IV gathered around 35,000 cleruchs, a number which included infantry and cavalry, and a similar number of mercenaries and Egyptian levies. Ptolemy IV’s conscription of 20,000 Egyptian infantry was a turning point in Ptolemaic military history, as it was the first time that the Ptolemids incorporated significant numbers of Egyptian into the phalanx.

#The situation in the 1st Century BCE, when the Romans arrived

Christelle Fischer-Bovet did the most recent book-length study of the Ptolemaic army (Army & Society in Ptolemaic Egypt), in which she used a range of epigraphic and textual evidence to trace the evolution of the Ptolemaic military. Fischer-Bovet pointed out that it is hard to tell whether the cleruchic army survived in any significant capacity into the 1st Century BCE based solely on Ptolemaic evidence, but that they were in all likelihood mostly inactive by the reign of Ptolemy XII. This means that although you had “cleruchs” who cultivated plots of land granted by the crown, they were no longer active soldiers in any sense, and the crown did not call upon them for garrisons or campaigns.

The Ptolemaic soldiers of the 1st Century BCE were also very different from their predecessors in that they would basically have all been born and raised in Egypt rather than being immigrants, they would have had no experience from foreign campaigns, and they were paid far less than previous generations because of their reduced importance. However, there is no reason to suggest that the organisation or equipment of the army would have changed much at all.

The last foreign campaign that Ptolemaic Egypt waged was the War of the Scepters in Syria between 103 – 104 BCE. The Ptolemids mobilised a significant levy of infantry and cavalry for this conflict, during which multiple Ptolemaic dynasts fought one another and their Seleucid rivals (Ptolemy IX raised 30,000 men according to Josephus which seems plausible enough).

This was the turning point when continual loss of territory led to political instability and loss of revenues. Here the importance of money to ancient states should not be discounted, a lack of funds was a very important factor behind the decline of Ptolemaic military power. Fischer-Bovet estimated a total military expenditure (army and navy) of 10,200 – 13,400 talents in wartime, and 4,500 – 5,700 talents in peacetime during the late 3rd Century BCE. For reference, the annual revenue of the Ptolemaic crown was 14,000 – 16,000 talents.

After the wearying internal conflicts and territorial losses of the 2nd Century BCE, the Ptolemaic army shrank in size and was being primarily used to suppress internal revolts or combat dynastic pretenders. Ptolemaic dynasts began to rely heavily on Roman support, and we know that the Ptolemids not only sent troops to support Roman allies, but many actually only returned to or maintained their grip on the throne because of Roman forces which had been lent to them. By the time Caesar arrived in Egypt in 48 BCE, the Ptolemaic army was in the middle of Romanising. Although Ptolemaic forces raised in Egypt continued to exist into the mid/late 1st Century BCE, the Ptolemids were becoming increasingly reliant on Roman troops.

There are some other good clues about the composition of Ptolemy XIII’s army in Caesar’s works Commentarii Di Bello Civili and Di Bello Alexandrino. According to Caesar, Ptolemy’s general Achillas fielded roughly 20,000 men and 2,000 veyeran cavalry. Caesar further states that this number included the Gabiniani, Syrian and Cilician mercenaries, exiles and condemned, and slaves. The Gabiniani were a Roman army acting as mercenaries for the Ptolemaic crown which included 2,000 legionaries and 500 Germanic and Gallic cavalry. These men had restored Ptolemy XII to the throne after his usurpation, and then simply chose to remain as Ptolemaic mercenaries.

Roman accounts across the board isolate the Gabinian forces as the largest threat to Caesar, despite the disdain which their disloyalty earned them. This is plausible given that they were the most veteran forces that Ptolemy XIII would likely have had access to, and that they were comparable in size to the army Caesar brought to Egypt.

It is unclear how many slaves and other condemned men joined the army or how they were trained and equipped, but it was evidently a sizeable portion of the army.

Besides several convicts and transports had been collected: for at Alexandria all our runaway slaves were sure of finding protection for their persons on the condition that they should give in their names, and enlist as soldiers (Di Bello Civili)

In the second chapter of Di Bello Alexandrino, it is again mentioned that Ptolemy XIII levied troops from throughout Egypt, and that he also pressed slaves into service:

[the Alexandrians] had sent deputies and commissioners into all parts, where the powers and territories of Egypt extend, to levy troops. They had carried vast quantities of darts and engines into the town, and drawn together an innumerable multitude of soldiers. Nevertheless workshops were established in every part of the city, for the making of arms. They enlisted all the slaves that were of age; and the richer citizens supplied them with food and pay.

Roman accounts allude to political rifts in Alexandria, in which the Alexandrian elite and the military elements they controlled to support their chosen dynast in the struggle for the crown. This suggests that a, presumably Macedonian and Greek, military elite that was powerful enough to shape dynastic conflicts still existed in Ptolemaic Egypt.

Would Caesar have faced some troops with similar equipment to those fielded by Alexander? It is likely yes, but many of the similarities stop there as the experience and training of these armies was vastly different. Overall it is hard to reconstruct a more detailed picture of the Ptolemaic army given the lack of evidence. The army Caesar faced would have been fairly diverse in terms of experience and training, and it included a significant portion of Roman troops.