A walling block for building with or without cement has a U-shaped profile with the curved top flanked by upper ridges onto which are located the lower flanges (9) of the next layer. The faces of the blocks have curved ridges with butt onto similar ridges on the adjacent blocks. A single ridge on one face locates between two ridges of the adjacent block. With the blocks stacked close together the butting profiles form grooves which can be filled with cement. The bottom edges have concave inner surfaces which sit on the curved upper surface of the lower blocks, and flat flanges with sit on the flat upper flanges of the lower blocks.
