the core is also useful when forming a column because vertical reinforcement can be inserted through the vertically aligned cores to lend stability to the columnar structure for example concrete grout and rebar steel pipe or post tension rods can be used to fill the core and strengthen the structure core 120 is generally rectilinear having walls generally parallel to the side surfaces on opposing inside corners of core 120 are located two interlocking elements 122 these elements extend the thickness of the block and project above the top surface of the block they are essentially co planar or parallel with the bottom surface of the block that is the bottom surface of the block is essentially co planar or contiguous with the bottom surfaces of these elements although neither the interlocking elements nor the core need extend the thickness of the block typically it is simpler to manufacture the blocks this way in any event the interlocking elements extend a distance above the top surface of the block this distance is sufficient to provide adequate interlocking between blocks when a second block is stacked on a first block block 100 has interlocking elements that are mirror images of each other on a diagonal plane of symmetry through the block these interlocking elements are positioned to permit the alignment of blocks directly over one another when rotated 90 degrees about the vertical axis of the block the interlocking elements also help to lock blocks into place thus adding stability to a.