"Mathematical Lens" uses photographs as a springboard for mathematical inquiry and appears in every issue of "Mathematics Teacher." Recently while dismantling an old wooden post-and-rail fence, Roger Turton noticed something very interesting when he piled up the posts and rails together in the shape of a prism. The total number of pieces, both posts and rails, was exactly right to form a triangular end with one piece on the tip and one additional piece in each row down to the bottom of the pile. He wondered whether this observation (that the number of pieces is a triangular number) would always hold for any similarly constructed fence consisting of two rails between each pair of posts and one post at each end connected by rails on only one side.