quote: 2. 3 levels of city walls: a. Barricades, available right off the bat. Costs 40 shields, doubles defense, doesn’t protect population. b. City walls, cost 80 shields, exactly like the current city walls. c. Fortifications, cost 120 shields, available with Labor Union or something. Doubles defense against conventional and Howitzer attacks, provides +50% defense against air attacks. Protects population.

Here is my alternative:
Small City Walls (masonry): Provides Infantry with +50% defence, protects cities of size <=6 against population loss. 40 shields. 2+ Garrison units required.

Large City Walls (masonry): Provides Infantry with +50% defence, protects cities <=12 against population loss. 80 shields. 3+ Garrison units required.

Small City Fortifications (gunpowder): Provides Infantry and Artillery with +50% defence, protects cities of size <=8 against population loss. 100 shields. 2+ Garrison units required.

Large City Fortifications (gunpowder): Provides Infantry and Artillery with +50% defence, protects cities <=16 against population loss. 200 shields. 3+ Garrison units required.

Keep (concrete): Provides 1 Infantry unit only with +100% defence, does not protect population. Not cumulative with city wall but applies when only 1 defending unit remains. Last unit of pop cannot be lost unless the keep falls. 100 shields.

Castle (engineering): Provides 1 infantry unit only with +200% defence, does not protect population. Not cumulative with city wall but applies when only 1 defending unit remains. Last unit of pop cannot be lost unless the keep falls. 200 shields.

How it works (assuming combat stacks in Civ3) Large city walls apply if defender has enough garrison. Once down to 2 units, the defender retreats to the inner walls (if any) and loses a pop point if population >6. Small city walls applies until one defender destroyed, then the last unit may use a fort/castle to further protect itself, but the city must at this point lose a pop point unless is size 1 (not cumulative).

With the advent of the Rifleman and Artillery, cities automatically provide defending infantry and artillery with +50% defensive bonus but all city walls and castles become ineffective against attackers with these troops. They can be sold for a 1-off production boost (stone used for building construction) or retained for a small fixed trade income (tourism).

I agree that with the introduction of missiles they become less usefull, but not obsolete. Not every civ will have a bunch of missiles to trow around.

I think trenches and bunkers can replacement both city walls and forts, and be built like an tile improvement.