A block for use in constructing a retaining wall having a bottom with a non-planar portion which creates a gap between the bottom surface and the top surface of a lower course of similar blocks when the block is placed thereon. This gap assists the block in resting on the lower course of blocks in a stable, level manner by providing a space where small amounts of rubble and dirt may exist without interfering with the stacking of the blocks. The non-planar, preferably concave, portion is also advantageous in that it reduces the unit weight of the block without significantly affecting the structural integrity of the block. Preferably, the block's bottom surface further comprises a plurality of grooves which further reduce the weight of the block and provide additional clearance in the gap for larger stones. It is envisioned that these grooves be “V” shaped, thereby having angled walls which act to funnel the larger stones into an area of adequate clearance when the block is being placed on a lower course of similar blocks.