Which fortification is for which troop?

I know some of them say they are defenses againt this type of attacker or this type, but I'm about to start raiding/plundering my first PC and I'd rather not waste troops on defenses I could just avoid by not sending them anyways. (If possible)

As such it would be nice if someone could break it down in detail.

Which block Mechanics, which block horsemen, which block infantry, what is consideered infantry, what's horsemen, what's mechanics? (I know some of these concepts are very basic, but I'd rather not make a mistake is someone explaining something to me that I SHOULD have known will avoid it.)

Thanks in advance.

right im no exspert but here goes

abitis are for slowing down enimy making archer towers more efective helps if you have some also they r for horse and scouts

rock falls are for mesheens and people

traps are for grould soulders

archer towers for any but meshiens

logs are for takeung out soulders to

There's the answer for the defensive side of things, but what about on the offensive?

What takes out defensive trebs best?
And rolling logs?
Archer towers can be wiped out by ballistae,
but it seems like the only way to take out traps and abs are by filling them with corpses