Firstly the surrounding MDF frame was given an undercoat and a couple of coats of flat black to act as a frame. Then I masked out the edges and covered them in news paper to protect them. I also marked out where all the buildings are going and masked those areas out as well, so that when I peel the masking tape off there will be black location points for each of the buildings.
Then I applied all the scree, and collapsed rubble at the bottom of the cliff edges and such like, and gave all the exposed rock a couple of spray coats of dark grey base.
Then a couple of layers of progressively lighter grey paint dry brushed onto the exposed rock faces and scree.
Finally a close up of the rock formation on which the fortifications sit.