Abstract: A set of construction elements for erecting three-dimensional structures comprises hollow structural members used either as posts or as longitudinal beams and also comprises hollow assembly blocks provided with a series of openings in different orientations. The projecting head of an attachment end-fitting mounted within the end portion of a structural member can be latched within each opening of the assembly block. The attachment end-fitting of each structural member is mounted for displacement in axial sliding motion within the interior of the structural member. A movable locking wedge is placed transversely within an attachment end-fitting and inserted through corresponding openings of the respective structural member. Rigid attachment of the structural member to the assembly block is achieved by clamping the edges of the assembly block opening between the flanges of the projecting latch-head of the attachment end-fitting and the end of the structural member.