The design of the bridges is complex. Each of the two decks is supported by inclined outward-leaning pylons. The decks are suspended from fans of slender steel rods called deck stays—there are 180 on each deck, made up of over of cable—and are held in position by other rods called backstays. Because the pylons lean the back stays are under tension. The deck is secured in place by steel collars fitted around (although not supported by) the pillars of the railway bridge; the collars are themselves attached to the bridge's foundations by tie-down rods. The entire structure is thus held in place by exploiting the tensions between the pylons and the various stay rods and struts.