Filter Beds The graphic to the right illustrates the appearance of one of three brick built filter beds in Tweedsmuir Camp. It has not been drawn to scale. Each filter bed is cylindrical in form and includes one pair of abutments on opposite sides. The space between each pair of abutments is back filled with earth. Both the abutments and back fill were used to shore up the structure's cylindrical wall. The second image is a photograph showing one of the filter beds. The yellow arrows point to a pair of abutments and the red arrows to earth mounds.