Of particular interest is Da Vinci’s work with bridge design for a range of practical and military purposes. Using no ropes, structural supports or nails of any description, Leonardo designed the emergency bridge. During military advances or retreats there wasn’t enough available time or man power to build a typical bridge, so Leonardo designed one which could be constructed and dismantled immediately using only saplings and a team of three or four people. This design uses the concepts of tension and resistance noted by Leonardo in other drawings. Strong, reliable and innovative.