City Wall Defense

Traps:

Can be cleared by warrior spam.
Archer towers and open gates with 1 unit of each or a force will help defeat this.
They can not hit siege weapons.

Abatis:

Deters Calvary spam to lower loyalty. Number range not really known. I personally have 1,000 per city. In end game, mostly useless.

Archer towers:

This is considered the best defensive unit we used along with troops.
All units can attack archer towers.
Archer Towers can not hit ballista even if you have level 10 archery and they have level 6 archery.

Ballista:

Range 1400 - Archery Science required is 6. (30% increased range.)
Basic Range: 1820.

Tower:

Range 1200
Max Range: 1800

If you are attacked by only Ballistas you must have gates open (with an army that can beat them) to win the attack unless they can not overcome your walls in 100 rounds.

Rolling Logs:

Can be cleared by warriors.
Reported to not hit siege weapons, I’m assuming ranged only are immune.

Rockfall:

Can be cleared by warriors.
Reported to not hit siege weapons, I’m assuming ranged only are immune.
Worse range than Rolling Logs.
Last defense to trip.