Abstract: A building block comprises a transverse groove (12) in each end face (10b, 10c), an opening (15) extending from the first (10e) to the second bearing face (10d) in which a longitudinal groove (13, 14) is also provided. The block is further provided with reference and positioning structure comprising a pair of longitudinal seats on the first bearing face and a pair of projections, each divided into three projection portions, on the second bearing face. When a building structure is constructed, the blocks 10 are superposed dry and in a staggered arrangement in superposed rows, such that the longitudinal seats of each block engage the projections on the blocks of the underlying row. The apertures and the grooves in the blocks constituting the building structure form a grid of intersecting vertical and horizontal channels which extend over the entire building structure, and in which a binder is poured and solidifies, ensuring that the building structure is stable and resistant over time.