Catenary

The roof-arch of this pergola is a catenary (the natural curve made by a slack washing line, or overhead power cable) turned upside down.  This kind of arch is often used 

in bridge design, as it is pleasing and very strong.  The arch here is supported 

by a thinner arch beneath, in the shape of a semi-ellipse.  

The overall construction can be very slender due to the strong design (and therefore difficult to photograph!) and provides an excellent support for climbing plants 

such as grape vine, clematis and jasmine which will form a shady, 

interesting and fragrant roof.

The width (span) of the arches can be up to 5 metres (17ft)

allowing a large area to be covered with the minimum of

visual obstruction.