Abstract: A system for the construction of containment walls or the like using a plurality of modular blocks each having interconnectable ends for laterally mating with like blocks to form secure joints. The blocks include a plurality of corresponding ridges and channels in the block's top and bottom surfaces, respectively, for successively stacking rows of the blocks securely and properly atop of one another. The modular block system also includes specialized blocks which are capable of being stacked to form right-corners or to laterally offset an otherwise straight wall to permit contouring to suit the needs of the user.