generalstaff
Steadfast
This brings me to my next suggestion:
In the future era it would be nice to have a building similar to the aforementioned ballista improvement, like a tesla coil (think red alert!), that can be built in cities and zaps adjacent units for 10% every turn. Upon discovery of perhaps another tech it could be upgraded to have a range of 2 tiles instead of 1.
Or alternatively occupied forts in the future (or even modern) era could have that option added to them, upon discovery of a specific tech, such that enemies suffer 10% damage when passing by next to said occupied forts.
Just brainstorming ideas here
My Towers module added several buildings like that: Cannon Tower, Artillery Battery, Missile Battery, Rail Gun Battery, Laser Battery, and Anti-Matter Battery. The names suggest the tech level. It also had several earlier "towers" which improved the Defense % and Reduced Bombard damage. It was part of my building pack which I did not update since 1.74.