Stone Lined Moat Walls
Most moats at castles these days where the walls are not lined with stone are covered in grass and shrubs to prevent erosion. Originally, these walls may or may not have been covered in grass. Simple walls of packed mud and clay would have been much more difficult for any attackers to climb but would have also been prone to erosion. In the case of plain mud walls, the angle of the wall was cut to about 45' to prevent too much erosion. They also mixed in clay to make the walls stronger and to make them slippery for anyone trying to climb up. In the case of grass covered walls the angles were sharper at 60' to make them more difficult to climb. You can see examples of both types in the moats pictures at the top of the page.