Originally posted by Mozzy:

Game max is 8 up and 8 down, for max differential height of 16 by terraforming earth 8 up while digging 8 down.

For trolls you need just tall enough to prevent throwing rocks over wall at your house. Assuming base ground next to wall is level ground - e.g. 0 , you need to raise wall ~7. 5-6 will allow troll to still throw rocks over wall and you can easily see their head and shoulders peering over the wall.

Raising earth is lot faster/easier than digging so you could do 7-8 up and be done, or extra insurance and 7-8 up with 1 down, 1 wide moat around the wall

I dig the moat down to water, but moat and wall defense is super effective. Wont stop flyers, but a lot less to worry about normally.