Mercenaries are soldiers of fortune; people who fight not out of national allegiance but for money. In Latin, they were called Mercanarii, meaning "hirelings".
Often veteran ex-soldiers, these skilled fighters sell their services to whoever will pay them. Mercenaries working as hired guards of the Ludus of Batiatus in Blood in the Sand and Gods of the Arena would wear what appear to be standard legionary armor, but were distinguished onscreen from Legate Glaber's troops by their black cloaks.
When the Praetor Gaius Claudius Glaber was charged with the supression of the slave revolt during the early months of the Third Servile War, he was given command over a temporary militia of up to three thousand men, rather than a fully instituted Roman legion, as the Senate did not yet view the revolt as a full on war. As the Third Social War (91-88 BCE) occurred less than two decades prior to the Third Servile War, Glaber's force may have been organized along the lines of the all but obsolete Alae Socii (allied contingents, or literally 'allied wings').
The ancient Greek term for mercenary was Mistophoros (plural Mistophoroi), which would have been common in the eastern Mediterranean during the Hellenistic Diadochi period. Aside from the waning powers of the Ptolemies in Egypt and the Seleucids of Syria, the Graeco-Persian Kingdom of Pontus in eastern Anatolia, ruled by the formidable King Mithridates VI, employed in his forces many mercenaries of Greek, Cappadocian, Celtic, Scythian and Thracian origin.
Celts from Gaul, Pannonia, Thrace and Galatia were widely employed in large numbers to serve as mercenaries in the Mediterraean states, from Carthage, the Seleucids of Syria and the Ptolemies of Egypt. There are reported instances of Gauls or Galatians serving the bodyguards of such rulers as Mithridates VI of Pontus, Cleopatra VII of Egypt and Herod of Judaea.
After Ptolemy XII Auletes was restored to the Egyptian throne by the Roman Proconsul of Syria, Aulus Gabinius, part of the Syrian legions, about 2,500 legionaries and auxiliaries, were posted in Egypt to uphold Ptolemy's regime. This force would become known as the Gabiniani, and would soon grow alienated from Rome as they adopted the ways of their Egyptian hosts, and had married local women, and their loyalties shifted from Rome to the Ptolemaic dynasty. This force would support Ptolemy XIII Theos Philopater after the death of his father. But they would be defeated by Gaius Julius Caesar during the Alexandrian War which last from late 48-early 47 BCE, after which Caesar replaces them with his own legions to support the reign of his own preferred candidate to the Egyptian throne, Cleopatra VII Philopater.
Ludus Guards[]
Little is known of the sort of private security employed at gladiator ludi. In the series, the guards at the ludus of Batiatus appear dressed as Roman legionaries, though they wear black cloaks and tunics, whereas actual legionaries wear crimsom-colored cloth. In history, ludus guards may have been former gladiators with no prospects outside their profession, and agreed to remain in their lanista's employment. Or they could be demobilized legionaries or mercenaries from outside of Italy. In any case, a large ludus with a number of slaves trained in combat would be run like a prison, and require the presence of a formidable security force to maintain it, at the lanista's expense. The fact that historically only 74 out of 200 gladiators managed to escape Batiatus' ludus is perhaps indicative of both the size and strength of ludus guards. A possible Latin rendering of their job-role might be Ludus Custodis/Vigiles Ludi, or ludus watchmen.
