This element is intended for making a border between a garden (9) and a lawn (10). It has the form of an elongate T, the leg (1) of which is situated practically half-way between and at right angles to the wings (2) and (3) of the T. The border is mounted so that the leg (1) of the T is at the level of the ground and turned towards the lawn (10) in order to allow mowing the lawn flush with the construction element. The element is preferably made of reinforced concrete or of asbestos cement. <IMAGE>