The invention is a composite masonry block having a front surface and a back surface which are adjoined by first and second side surfaces, as well as a top surface and a bottom surface. Each of the side surfaces has an inset extending from the block top surface to the block bottom surface. The block top surface has one or more protrusions positioned adjacent the first and second insets on the block top surface. The block also has a protrusion which has an angled side wall, the angle being at least about 20.degree. from vertical. The protrusion is positioned on the block so that it will mate with any opening of an adjacently positioned course. In use, the blocks may be stacked to provide an interlocking structure wherein the protrusions of one block interfit or mate within the insets of another block.