I need some help with roman mercenaries

[Bryan]

both Constantine and his opponents hired Goth's, Frank's and Alamanni mercenaries.

Your mention of Constantine hiring Goths and other Germans reminded me of another situation that may be relevant to mercenaries: didn't Marius hire gladiators for his army during Sulla's first civil war? I know there's a point that could be made that the Marian forces were ad-hoc legions (and therefore state forces, not mercenaries), but could you instead make the point that they were mercenaries? As in apparently not enough Romans were invested in the Marian faction's cause, and therefore Marius and Cinna and the rest had to hire troops because they could not raise legions. I believe Marius' forces behaved quite badly and Sertorius had to send his troops into Rome to bring them to heel.

This might be a thin argument to make, now that I've written it out like this. I suppose it would depend greatly on what definition you're using for "mercenary," as several others have already mentioned.

Marius raised an army of slaves he freed on his return from Africa to Rome, who he promises freedom in exchange for loyal support. Referred to as the Bardyiae, they were normal farming slaves not gladiators.

Although gladiators were used by Marius and others as bodyguards, even while on campaign, as well as the use of lannista as trainers for the legions following the reforms of P. Rutilius Rufus and later Marius.

[Gunthamund Hasding]

well if you look deeper you can find all sorts of troops that will qualify as a kind of mercs but none in the "classical" meaning of the word

as we progress through the Principate and the auxilia begins to be rather a "normal" heavy infantry unit and the cavalry will also tend to be heavier, numeri units were employed this were allied troops from outside Rome borders, example: numerus maurorum (cavalry) or numerus palmyrenorum (archers generally) which were deployed by Trajan in his Dacian Wars numerus surorum sagittariorum

This numeri would fall more likely into the "mercenary" role

you can find some infos here:
A Companion to the Roman Army, Paul Erdkamp Blackwell Publishing Ltd 2007 page:195
https://books.google.co.uk/books/about/A...YMAC&hl=de

"Numeri are often regarded as “irregular” units, but that is only because they lacked
the more standard organization that legions and auxiliaries had."