A horizontal trellis is a type of structure used to support climbing plants. It is similar to a PERGOLA, which is a structure made of vertical posts and horizontal beams that form an open lattice. The difference between a horizontal trellis and a PERGOLA is that the trellis has a flat top and is usually made of wood or metal. The trellis can be used to create a shaded area or to provide a decorative backdrop for a garden.