Abstract: A composite structure finding principal utility in the formation of walls, floors, patios and the like, for example. The structure is made up of a coplanar assembly of slab-like flat-faced elements provided with knobs and sockets that are congruent with each other as well as being congruent throughout the total structure so as to provide positive interlocks among the elements and thus eliminating the need for adhesive and like binders. The elements may be of molded concrete and relatively light weight so as to facilitate handling on the job by the ordinary artisan in the building of a patio, for example, in the elements are coplanar on a bed of sand, etc. The elements are furnished in several groups in which each group contains several identical elements. In addition to the knob-socket feature, the elements have perimetrical outlines or configurations such that side-by-side elements abuttingly match each other as to contour.