Pergolas existed back in Roman Pompeii, supporting vines which grew happily over them. At West Dean garden, Sussex, there is 300ft long pergola constructed with stone pillars, and resplendent with many varieties of Wisteria, Roses and Clematis.
The structure may vary but the general purpose is the same. Pergolas provide height for climbing plants, shade to sit in, and act as sight lines or as a visual barrier. There is also little better garden experience than walking under a flowering Wisteria or Rose, and being enveloped in their gorgeous scent.
Often, pergolas have a pseudo-Japanese feel about them, but they can convey far more than that. With substantial oak legs and beams, they are redolent of the sights and sounds of large Edwardian gardens. Using plain timber, with little or no ornamentation, gives a really striking, modern look.
For a different appearance, metal tubing could be used, perhaps in ultra-trendy Corten steel. This material forms surface rust of a true rusty-red colour, without it eating away inside to weaken the structure.
However it is built, a pergola must be tall enough for someone to walk under without becoming entangled in the roses above. Width depends on the purpose. Sometimes a narrow tunnel effect works perfectly, others need to be wide to calm down the view.