When constructing a mortarless block retaining wall, the maximum height that you can build it will depend on some factors. One such factor is the kind of blocks that you use. These blocks interlock with each other, so make sure to follow the specifications of the manufacturer as to what height the blocks can handle. Another consideration would be the type of soil. Softer soil will mean more lateral pressure, meaning the height of the wall will be limited. You will be able to extend the height a little bit further with harder soil. Also, as a rule of thumb, a block retaining wall over 4 feet will require extra reinforcement.