Fencing...

[Alex Koponen]

   Wood fences and walls are much easier to construct but require a great
deal more maintenaince than stone or brick. In rocky terrain many farms end
up with stone walls around their fields after a few decades of removing
stones from the fields.
    For city walls many in the bronze age used sun-dried bricks. After
development of catapults and other siege equipment this was no longer
adequate.

  --  Alex K.