Walls

This summer Evony was modified so that the height of the walls provide a big boost to defense. Now each level adds 5% to range for both the fixed defenses and the ranged units, when you have the gate open. So you get a big free shot at your enemy if you have the same level of archery.

Bottom line is that the height of walls, and your level of archery are really important.

Remember if gates are closed then your army is safe, but they don't help defend your city. If gates are open, they defend along with fixed defenses, but they can get killed.