If you want to be really obsessive, could go full on with a unit list. Like, Caledonians (who, I'd like to divide Caledonia in 2 in that case, and give them the northern most part):

Divided into two groups, the southern, more Briton-affected, and northern wild hillmen; most names in English just for the joy of it
1. Tribal levies
2. Southern skirmishers
3. Northern skirmishers
4. Horsemen
5. Orcadian spearmen
6. Northern spearmen
7. Southern spearmen
8. Southern shortswordsmen
9. Northern axemen
10. Mahrauron (southern champions with swords)
11. Ymryh (southern chariots)
12. Northern hill horsemen
13. Two-handed axemen in the north (eh, there were a few big axes there, probably just wood axes)
14. Northern shortswordsmen (which would be extremely expensive, swords were very rare in the north)
15. Slingers
16. Archers
17. Selgovae archers (camoflauged themselves)