A covering comprising a series of modular elements (2-9) that are sequentially telescopically nestable and movable by means of a drive mechanism along two tracks (10, 11) into an extended covering position or a retracted uncovering position. The drive mechanism includes cable lengths running along the tracks (10, 11) at the base of the modular elements (2-9) and passing around pairs of pulleys in the modular elements (2-9). Two respective cable lengths are subjected to a retracting pull by a pulling mechanism to bias the elements towards the uncovering position, and two other respective cable lengths are subjected to an extending pull by the same pulling mechanism to bias the elements towards the covering position.
