Here are some basic wall formulas...
HP = 100 + 50*Wall Level
Armour = 15 + 8*(INT(Wall Level/3)) <- INT is round down the result.. 1-2 = 0, 3-5 = 1; 6-8 = 2; etc.
Damage is a bit trickier.. there are 3 classes depending on wall level:
Walls 1-9 = "Ballistae"
Damage = 10+2*Level; Accuracy = 30%
Walls 10-19 = "Catapult"
Damage = 30+5*Level; Accuracy = 50%
Walls 20+ = "Mortar"
Damage = 50+10*Level; Accuracy = 80%
So basically Level 1 and 2 walls have 15 armor.. and since a Hoplite does 18-21 damage.. they can hurt the wall.. 30 phalanx (an entire stack) does 90-180 damage to these walls each turn. Steam Giants Have are capable of doing 72-75 damage and thus can even damage up to a Level 11 wall. Strangely enough cooks do 30 damage, so they can hurt walls too
2. Artillery can most CERTAINLY damage frontline units.. and they do a good job at it too tending to kill every unit they hit.. plus they fire first.
3. Defending ranged units can most certainly hit frontline troops while the walls are still up.. all the wall does is take up the fronline spots until the sections are destroyed. Basically, the attackers' frontline must bear the artillery and ranged fire from the defender for as long as all the all sectiosn remain.. as each section gets destroyed, they are filled with defending troops.
Screenshot links:
Round 1
Round 2
There really is no "before" and after.. as each picture is taken at the end of the round (before Doctors do their healing), but it clearly shows 3 wall sections in the front row.. and them dying over 2 turns.. if the defender would of had any units in town, they would have filled the empty slots available.. this means ranged slots, artillery, air, support and fronline when those open up (like in round 2).. the only slots that will not be there are the "flank" slots which only come into play after ALL sections are destroyed.
Think of wall sections as "big units" that take up the entire slot.. it will make much more sense that way.
Edit Signature
Sweets
the most annoying person you will ever not meet