Here's an update on what's happened since I last reported on the situation:
Cassiel has lost all but one city, which is in the middle of a bunch of other enemies, to the west. I took a total of 8 cities from him (and retook the one which I temporarily lost).
The continent I'm fighting on is a long one, and I started in the far east of it. I now control everything east of some natural barriers, except for territory held by Capria (who is my friend).
Morgoth, who is on an adjacent continent to my east, agreed to a peace treaty a while ago - the only combat on that front consisted of him sinking some fishing boats and me lobbing fireballs at his closest city from across the water.
The natural choke point to the west consists of a lake (at the north part of the continent), a bunch of impassable mountains (south of the lake), and then a small two-tile-tall hilly passage with a city belonging to Rhoanna (until I captured it).
Conveniently, Rhoanna and Os-Gabella both declared war on me, so I have begun rolling into Rhoanna's territory.
Unfortunately, Arendel Phaedra also just completed the exhalted version of the altar. Her territory is on the westmost part of this continent.
Rhoanna had the most powerful army in the world prior to her declaring war on me, but I destroyed fully half of her entire army in the last two years, leaving no significant obstacles to my conquering the continent (except for lack of strong soldiers to guard the cities I take).
My army has 7 confessors who cast ring of flames, which is enough to completely destroy anyone near the army, and Sphener (level 11) rips to shreds any horsemen who dare to attack the army.
But here's what I expect to happen:
1. I will likely conquer the entire continent, destroying all five civs there who were foolish enough to declare war on me. (Capria remains because she hasn't backstabbed me)
2. Falamar or Perpentach, who are on the other side of the world, will build the Altars, so I will lose anyways. I have virtually no navy, and certainly no capability to cross oceans.