Abstract: A system of modular, hollow interlocking building elements which can absorb large horizontal or vertical pressures, and thus eradicate or minimize the effects of active pressure. The elements can be connected along each face and stacked one upon the other to form a stable, continuous, multi-directional structure, requiring no cement or other stabilizing material. The system comprises a plurality of base elements, having on slits on the vertical faces, and a plurality of interlocking elements to form layers above the base, having a slit in each of two, three or four vertical faces. The elements are arranged so that the faces having no slit form the outer surface, thus forming a structure having a smooth, continuous outer surface. The elements can be filled with any required filling material. The elements may be used in construction of structures in which active pressure is a factor, such as retaining walls, bridge abutments, ramps and the like.