I like the idea of forts as well. I think they'd be justified simply for the RP fun factor. Forts and Castles are just plain cool! But they are also significant battlefield assets which could add interesting possibilities to the tactical play. To quote Brad... "Elemental is a strategy game that takes place in an RPG world." I think castles and forts, fit well the bill of strategy and RPG.
I'd want to see Caravans expanded to support fortifications. Providing a supply route which must be protected from enemy disruption, or the units within will weaken (perhaps the existing Morale feature could work for this). This gives the enemy some options to defeat an uber turtle point. And it adds a balancing cost, while also making Caravans and roads even more purposeful. I'd think that fortifications would increase unit defense, allow a slow heal rate, and project a limited zone of control which includes range support and gives a Morale or other stat boost to nearby units. I don't think that the building of units should occur at fortification sites. Fortifications would already have enough boni. Possibly including...
Fortifications could also impact random events in such a way as to make event resolution more dynamic and interesting (more on the dynamics in paragraph 3). Fortifications could reduce/increase the odds for certain events to occur. They could also randomly trigger quests. An impressive Castle within the badlands might encourage a band of wandering nomads to settle down (added prestige or recruit non-hero units). The presence of a remote wildlands fort might randomly trigger a quest to track a rare Griffin. But the existence of a fortification might also perturb some unknown Sovereign who leads a covert attack on it (randomly generated units of no known allegiance). An abandoned or otherwise unkempt fortification might become infested with a monster colony which expands to threaten the countryside. Or the presence of a pre-existing fortification turns a rolled negative event into something positive... instead of dealing with a random bandit event, the player instead gets a positive event as the citizens celebrate their Sovereigns foresight and wisdom. And on and on... Fortifications provide more event fodder.
The building of fortifications could also be used as one of the possible responses a player makes to certain random events: such as bandit raids, civil uprising, and creature spawns. Bandits start raiding a city from a nearby lawless region, so you decide to build a field base to exert some control over that unsettled region. Hostile creatures have colonized nearby and are spawning in great numbers to murder your citizens. Something must be done. You have a choice: attempt to protect the citizens by stationing more units in the city, invest a little more and send out extermination parties, or go all out and build a fortified hunting camp.
And instead of solving random events with static and predictable event resolutions; Each choice could instead impact RNG odds. Having dynamic odds would keep things interesting. Otherwise, players will 'learn' the best route to take when they encounter the same events again. Terrain and a variety of other variables might be used to give the player a clue as to which option is best for each specific event occurrence. This gives the player more reason to choose one option over another. Such as: garrisoning extra troops within a city might generally be an effective and cheap pest control method when the creatures have nested in, and attack from, open grasslands. But the greater number of global infestations, the tougher it is to deal with a regional infestation. And/or the more fertile land a region has, the easier the extermination. etc Then also, a player might be in a situation where they don't want to risk even good odds, so maybe they play it safe and spend a bit more to send out organized hunting parties instead of the cheaper option of garrisoned troops. And maybe the creature dens are located in a nearby dense forest, but a player decides to gamble on even odds that hunting parties will be able to do the job. But perhaps even a normally ballsy player would want to construct a fortified hunting camp to deal with creatures spawned in particularly difficult terrain such as swamps, jungles or mountains.
I think adding RNG odds to random events would make things more interesting. But the player needs clues so they can make informed decisions, take calculated risks, and just generally have more motivation for selecting one choice over another when dealing with random event resolution.
As happens in my brainstorming sessions, I travelled a tangent. I don't expect that fortifications would make it into the core game in all the ways we might imagine it. Elemental IS an epic game, and it allows for Lots of growth. But Fortifications is one of those things that I think it might be worth it for the developers to code in a module for, even if fortifications don't make a big presence in the vanilla game. A fort module opens the door for all sorts of possibilities. Who knows what creative ways people will find to tweak a code base for forts. Perhaps in a game where the entire world map represents one modern city; Forts might allow for corporations or something. In space mods, forts might make the perfect foundation for star-bases. etc. I think it might be helpful to the community if a fort module was created which allowed for the turning off and on of various things... Caravan required, resource gathering, bonus and penalties to unit stats, event and quest triggers, diplomacy modifiers, and ??