In essence an arbor with an open roof, a pergola is an excellent idea for giving presence to a part of a deck or garden that lacks visual interest or highlight a special feature such as a spa or conversation area. The rafters and crosspieces that are so prominent in many pergola designs can also add height and mass to an otherwise flat portion of the deck. Often, pergolas are intended to serve strictly as decorative or architectural elements in a deck design. With a few minor changes to the open roof system, though, and perhaps the addition of a climbing vine or two, a pergola can become a dramatic overhead shelter.
A pergola can also employ a series of separate vertical structures tied together visually with a band of horizontal boards at the top. This elongated design works well to unify different areas of a deck, delineate a walkway, or give an impression of a roofed passageway from one part of the garden to another. When laced with greenery overhead, it can take on the feeling of an arbor.