A Guthrie rolling bridge was a kind of retractable bridge, an 18th century version of the drawbridge. It was commonly installed as the access across the narrow steep sided ditches characteristic of the polygonal forts of this era.
Rolling bridges were unhinged, and remained horizontal as they were retracted within the gates of a fortification [1], similar in operation to a modern thrust bridge.
Two such bridges are installed at Fort Nelson, Portsmouth, United Kingdom.