You can also try to make a whole wall using a terrain. You can even build a piece of wall stone by stone and lay it on the groundplane (the side of the wall that will be visible pointing at the sky) and make an altitude render from the top-view. Use this altitude render as displacementmap on the terrain and you'll have a whole wall made from one terrain. It'll save you lot's of memory and polygons.

(_/)
(='.'=)
(")(")This is Bunny. Copy and paste bunny into your signature to help him gain world domination.