Bricks, Masonry, Asphalt and Concrete - building a retention wall

I would like to build a retention wall to level out a sloped area to the rear of our house. Initially I had thought about using 6"x6" treated lumber for this, but certain areas of the retention wall are about 24 inches high, and I'm concerned about stability of a wooden wall given these measurements. Does anybody have any experience using prefabricated block for use in building retention walls? Any tips? Any other suggestions? Thanks.

I am not sure how wide and tall your wall is going to be but start with a footing. This is key to building a solid wall. You may also consider reinforcing it with rebar that projects upward from the footing if your holding back a significant load. Your first course of block can be positioned before the concrete drys but make sure it is level and that their is exactly 3/8 of an inch of space between each block both vertically and horizontally. If you get the first course down nice and level let it dry and from then on it should be easy to build on top of it.

I found an Oldcastle retention wall system at Lowes which is being delivered today. It suggests a good, level base, but concrete is not required.