I think I just found a sweet unit

[Kryzantine]

Go conquer Southern Ireland, and upgrade the local levy. The final tier has some elite spearmen, the Dubosaverlacica (Ebherni Armored Shock Infantry). They're really expensive, however.

Thing is, these guys have some insane combat power. A unit without any experience whatsoever suffers minimal casualties. When I sieged the other Irish city, I sent these guys in, and out of the 120 men, only 3 died. When used wisely, these guys will hold off any enemy for an extended period of time.

I just fielded a few more units, and these are truly the elite of the elite units. I won't have to worry about getting some true heavy infantry again.

[Admetos]

Wait till you try out the Gaesatae then...

[rhetoricalcalvary]

My friend and I made a custom battle of two full stacks on even, unbroken ground. One army was those Irish guys and one was all Spartan hoplites, and the Irish guys won! No particular "tactics" were used, we just ran them together (much like an ancient hoplite battle would have gone anyway) and after 10 long minutes, the Spartans had been whittled down and broken.

[Solar]

If you're Lusotannan, you can also train Dosidataskeli (Vasci Armoured Sock Infantry), which look pretty similar and are actually marginally better (better armor and some extra attributes) than then Dubosaverlacica. I've a couple of these in my army in Gaul which I use to plug eventual holes in my battle lines, and they hold off pretty well against pretty much anything.