the invention provides a new fence system permitting the construction of privacy fences ; perimeter fences ; boundary fences and rail fences using a small number of different fence elements . these elements consist of a hollow elongated post / rail element of semi - octagonal transverse cross - section ; an end cap for the element when used as a post ; an l - shaped connecting bracket ; a panel element and an end cap therefor ; a clip for fastening panel elements to the rails ; closure elements for the rails and posts that also locate and hold the panels when they are engaged in slots therein . the panels are provided near to their center with a plurality of spaced stiffening walls to resist buckling under heavy loads .