The present invention provides a block useful in the construction of walls and structures that is shaped in the general form of a rectangular solid. A horizontal channel extends along the entire length dimension of the block, open coincident with the top of the block. An open vertical channel associated with each end faces outwards toward an adjacent masonry block end. A protruding portion extends from the flat bottom with the same width of the open channel on the top, so that an interlocking connection is formed. A protruding rectangular portion is optionally incorporated into the front face portion, and also optionally into the rear face portion, leaving a recess along one end, and along the top, so that when assembled into a wall, the recessed parts of the face portion give the appearance of mortar joints. Vertical and horizontal rebar may be set within the aligned channels of the blocks when assembled into a wall. The blocks do not require excessive lifting when assembled to a wall or structure to clear vertically aligned set rebar.