Abstract: A prefabricated wall structure for forming an enclosure such as a horse-box has two spaced tubular uprights defining an opening therebetween which can be blocked by a door. A crosspiece extends from one post, across the opening, beyond the other post and is secured to a wall section supported by the other post. The crosspiece gives rigidity to the structure. Each post has a substantially square cross-section and has fixing holes provided in the end portions thereof. The crosspiece carries mounting means which are inserted in the upper end portions of the posts and engaged by screws extending through the fixing holes. A door for closing the opening can be supported either by one of the posts or by the crosspiece.