Disclosed is an economical and effective way of producing a modular retaining wall, using only blocks which in and of themselves are of insufficient thickness to function as retaining wall blocks. The modular wall includes backer blocks and facing blocks which are connected by connectors in a back to back, spaced apart arrangement, thereby forming a hollow retaining wall. The hollow wall can be filled with loose filler material to increase the mass and retaining capacity of the wall. 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 of retaining walls and freestanding, double sided, decorative walls forming both straight and curved walls.