From Buckles #3

Those jacks must be 12' tall. The square things are back rests that fold up (starbacks). I remember hearing that when dismantling, the stringers came down with such force, they were caught by men wearing  pads on their shoulders. So this leaves me to believe that the Barnum & Bailey seating arrangement (now owned by the Ringlings) had a conventional grandstand with chairs, these starbacks and finally chicken roosts for the financially challenged.