Disclosed is an economical and effective way of producing a modular retaining wall for a material to be retained, using backer blocks and facing blocks which are stacked into continuous front and back wall components connected by separate connectors in a back to back, spaced apart arrangement, thereby forming a hollow retaining wall. The hollow wall is filled with loose filler material to increase the mass and retaining capacity of the wall. None of the wall components is embedded in the material to be retained. The facing blocks, connectors and filler material are all separated from the material to be retained by the backer blocks. Further disclosed are wall components and a wall kit for a modular retaining wall. A double sided decorative wall is also disclosed. The modular wall system allows for the construction both straight and curved retaining walls.