This has been discussed a bunch of times during AoW 3 development.
Basically, garrisoning cities is a pointless micromanagement hassle. Because cities don't have base combat strength (as they do in Civ) and they don't have a default garrison (as they do in TW). They can be captured by a single scout.
A couple guys pointed out you can always build a couple defensive units, but this is inefficient, because a city can only build one unit at a time, any time a city is building a garrison, it cannot build an offensive stack. Due to the opportunity cost, a city cannot defend and attack at the same time. And it's usually better to attack because attacking stacks can group up.
There needs to be buildings that spawns Garrison units over time. These units would have reduced upkeep but cannot move from the city. A tier 1 wall would provide up to 3 free militia type unit for instance. and a tier 2 wall would provide up to 3 t1 ranged unit with 1/4 upkeep. A ranged unit upgrade building (this game's version of shooting ground) would provide one t1 class ranged unit per level of population at 1/2 upkeep, etc.
Spawned unit would be seen on the strategic map, and they are replenished automatically one per turn. This essentially gives a city a second automatic build queue for defensive units, and remove the hassle of having to defend against scout capping.
Finally, because of the sector system, city spam would be capped anyways so there is no need to worry about that.
Basically, garrisoning cities is a pointless micromanagement hassle. Because cities don't have base combat strength (as they do in Civ) and they don't have a default garrison (as they do in TW). They can be captured by a single scout.
A couple guys pointed out you can always build a couple defensive units, but this is inefficient, because a city can only build one unit at a time, any time a city is building a garrison, it cannot build an offensive stack. Due to the opportunity cost, a city cannot defend and attack at the same time. And it's usually better to attack because attacking stacks can group up.
There needs to be buildings that spawns Garrison units over time. These units would have reduced upkeep but cannot move from the city. A tier 1 wall would provide up to 3 free militia type unit for instance. and a tier 2 wall would provide up to 3 t1 ranged unit with 1/4 upkeep. A ranged unit upgrade building (this game's version of shooting ground) would provide one t1 class ranged unit per level of population at 1/2 upkeep, etc.
Spawned unit would be seen on the strategic map, and they are replenished automatically one per turn. This essentially gives a city a second automatic build queue for defensive units, and remove the hassle of having to defend against scout capping.
Finally, because of the sector system, city spam would be capped anyways so there is no need to worry about that.