The news might be carried by magical creatures, announcing this publicly in every bigger town in these lands, and spread further through chatter like wildfire. A war between the Gods is something that does not happen every day! (I hope it does not in your world.)Motivation:
- loot from the battlefield (well it has to be mentioned)
- looting the city ( #3 of course, maybe even #2 ) and general killing, blood lust
- various vendettas and revenges, this being the final place to solve them
- people that actually live in the city/surroundings, and want their side to win
- being a follower of one of the gods makes you a fine candidate
- If the city is important (and it probably is), many will want to intervene, possibly even other gods. The rules don't say a word about other gods. Anybody read the Illiad?
- repent for their sins, undo the mistakes done beforeVarious:
- There can be a special 'force-field', that prevents any member of the armies to leave.
- It is forbidden to use godly powers to make soldiers change sides. But bribing, threats or even torment may be used on enemies, even captured ones if there are some.
- The creatures should reflect their respective gods, be not too powerful, but certainly unique. Anybody ideas?
- The creatures will sense without error, whether a soldier is a part of the army, or not.
- The war will probably take a while, and the soldiers need to eat, right? Smart traders will note the trading possibilities. Food, weapons, oil, any kind of equipment may be needed.God #1: Even if a stone is strong, it can be pushed aside or walked around. But take many stones, and build a sturdy wall out of them, and no one will pass!
Possible power: His army has a permanent blessing for everything they do cooperatively. Excelling in defense mainly, smart troop movements can give bonuses even to attack.
It may be a part of his powers, giving tactical bonuses for terrain and combat knowledge. OR, it may be a secret influence of some other good-aligned deity...Plot hooks:
- Never forget treachery. Hiring the players to kill that key magical creature, while the action is on the battlefield, is definitely not against the rules. Did I mention that being hired makes you a part of that army, too? Then you must stay until the very end.
- Some soldiers may want to survive, and don't want to fight for any side. (Many will join hot-headed, later realising what war is about.) They seek protection, because they can't leave the battlefield.
- Even if the characters do not want to intervene initially, will they, once the numbers dwindle from thousands to a few hundred combatants total? The reward would be great. But making one (or two) gods angry, hmmmm...
- General lack of armed folk may do anything from increasing the crime rate, up to calling an invasion of some foreign power. Very ironical if they worship some wholly different god, one that supported this theatre for own ends. And these gods and their armies are bound to one place. Sure, the winner gets the city. Smartie gets the rest.