Working with you to determine the desired height of the wall and calculating the number and size of stones required. Digging a trench twice the width and to the required depth for a proper foundation. Laying down the landscaping fabric. This vital step keeps plants and weeds from growing under the wall and pushing it out of level. Installing the gravel base. It will be at least 2” deep depending on how high your wall will be. The contractor will ensure the base is level with some sort of compacting device. The armour stones are stacked one on top of the other. They will likely be set with each tone slightly behind the other so that the lip built into them can lock into one another when the ground pushes forward against them. The weight of the armour stone itself, this lip, and the angle of incline are what keep the wall in place and the ground held back.