Wall mechanic?

Are there ladders?

What will happen to units fighting on top of wall if it collapses?

Nothing if i am not mistaken

I am not sure if they were ejected but in a stress test I saw them just fall to the ground unhurt when the wall went down.

No friendly fire.

Units magicaly survive at your own buildings colapsing or enemy buildings.

They just drop to the ground with no further effect (no damage done to them, no stun).
See for example Ornlu playing the third norman campaign mission (spoiler alert, obviously).

There are no ladders. Units enter through a wall-tower backside or a gate backside (you can flip the gate when placing it). They can also enter once a wall piece is destroyed by climbing up left or right onto a neighbouring wall piece (which ornlu never utilizes in the above vid… dirty casual :grin:)

There are also siege towers. Never saw them in action though.