Students at Missouri's Truman State University got a cool lesson in in a class about Leonardo da Vinci: a chance to turn his sketch for a self-supporting bridge into a working version.
Via their site:
The design was proposed by Leonardo in an undated drawing which appears above. In the drawing, Leonardo envisioned a bridge which could be put together very quickly using readily available materials (in this case tree trunks) and which could be disassembled just as rapidly. Although the version on the Quad will have some bolts and other reinforcements for safety purposes, Leonardo's design holds together and supports significant weight without the use of any nails, bolts, or other fasteners; it uses only the notches in the logs and the bridge's own structure.
Leonardo likely had a variety of applications in mind for this design although it would have been particularly attractive for military uses (other drawings on the sheet relate to cannons). An advancing army could use trees found on site, put the bridge together in a matter of minutes, and then–once used–could pull on strategically placed ropes and the bridge would come apart. The components could then either be taken along or allowed to fall into a river or ravine below and swept away. For more on Leonardo's mobile bridge designs, please see this National Endowment for the Humanities essay by Leslie Geddes.