Modular block walls have become very popular in the Southeast. They are the most common retaining wall constructed today. As you can see by the pictures, they are very attractive and the blocks come in many sizes, textures and colors. Modular block is used to build small walls to boarder gardens up to massive walls used to support entire building complexes. These walls are made of concrete but not all concrete blocks are made equal. The amount of load the wall must restrain and the environmental conditions the block must withstand will determine the grade/quality of the block that should be used.