The 400

[Agema]

It depends on turn. 400 average units would cost around 4000 gold and under 300 upkeep. That's probably feasible by turn 10, and it's easy by turn 20. Also bear in mind mages provide 10 supply per level of nature magic, and Tir Na Nog has plenty of nature magic. Many provinces can provide 300+ supply. Also, you get a supply bonus from nearby friendly castles.

To defeat large armies, you could try:
a) an army about the same size
b) a smaller but still large army with much better troops
c) quite a few thugs/SCs who can kill large numbers of enemies each
d) a decently sized army with much more mage support or thugs/SCs.
e) a few mages casting huge, powerful spells that wreck everything on the battlefield (e.g. rain of stones, earthquake)

[Rookierookie]

A few Ancient Ones with Protection boosted to 20+, some AOE weapon, a decent shield, regeneration and good reinvogoration, and preferably a Horror Helmet as well.

Or just have 3-4 mages with Summon Earthpower - Blade Wind.

[rdonj]

Couple the bladewind with ironbane for better results.

[MaxWilson]

Blade Wind + Iron Bane doesn't do much more than just Blade Wind, since it needs melee blows to break armor and your mages won't target anyone in melee with your own troops. I.e. they both work, but they don't synergize.

If you're EA Agartha, don't forget to spam Magma Eruption from your F Oracles. It scales really nicely with your high E. And I also second the call for Earthquake at Evoc-5, given that all your troops are high-HP.

-Max

[rdonj]

Really? I would have thought that since the bladewinds do physical damage it would have applied. I guess not. Phooey