Comment by gerdesj

The Roman empire at this time made massive use of auxiliaries - ie not Romans. These are soldiers from conquered lands. Mercenaries were also used a lot. Mercs are soldiers for hire rather than hired soldiers!

Auxiliaries might be closer to slaves than soldiers and mercenaries might have fewer rights than auxiliaries. The devil is in the details. Auxiliaries might be granted Roman Citizenship at commencement or after a period of service.

In general the policy was to deploy aux. from the other end of the empire to augment your top troops in a particular war theatre. Mercs were used to top up if available - think of them as Uber or Lyft when you've run out of decent taxis 8)

Ideally you'd expend your aux and mercs carefully, to keep your real killers (heavy infantry) going. However its just not that simple, depending on what you (Roman General) had at your disposal in terms of troops. It also depended on you not being daft and throwing your cavalry up hill at pointy sticks or whatever. "Skirmishers" can also be devastating:

The Germans (have a look at my username - yes I'm English) german - might mean spearman (I was told this by a bloke from Bayern). They were skirmishers - no armour and a big pointy stick and a buckler shield. They brought low several Roman legions.

Anyway. The term Legionary is a tricky one. And so is German and quite a few other terms here.