As noted, current military building upgrade path does not require any changes to the building system.
Barracks +1 Armory +1 Mil. Academy +1 plus base garrison of 1, you can foritfy 4 units in a city.
And yes, I do like my own idea of making them not cost maintenance while inside the city.
This also solves the problem of AIs not having any units once you blow away their attacking force. it won't cost them anything to fortify some in their core
Further idea, don't just bump up a city's defense if you fortify units. Increase HP by 1/2 the unit's HP.
For calculation's sake, so a city doesn't implode if a unit leaves it, units will always take damage and die before cities take damage. And yes, this may be overpowered if players can use a unit factory strategy to reinforce a city *may need to be adjusted* but I think the basic idea of units increasing a city's HP is a good one.
This avoids the situation of a unit leaving a city and putting the city at 0 health.
Barracks +1 Armory +1 Mil. Academy +1 plus base garrison of 1, you can foritfy 4 units in a city.
And yes, I do like my own idea of making them not cost maintenance while inside the city.
This also solves the problem of AIs not having any units once you blow away their attacking force. it won't cost them anything to fortify some in their core

Further idea, don't just bump up a city's defense if you fortify units. Increase HP by 1/2 the unit's HP.
For calculation's sake, so a city doesn't implode if a unit leaves it, units will always take damage and die before cities take damage. And yes, this may be overpowered if players can use a unit factory strategy to reinforce a city *may need to be adjusted* but I think the basic idea of units increasing a city's HP is a good one.
This avoids the situation of a unit leaving a city and putting the city at 0 health.