The unique structure of this bridge holds itself together without any fasteners or connectors. The parts are notched for easy assembly, just slip the notches together and build this sturdy bridge in a matter of minutes.

How can it do this without any glue, screws, string or nails? Sometime around 1485-1487, Leonardo DaVinci devised a method for building a self-supporting arched bridge that doesn't require any ropes or other fasteners. The bridge's own weight keeps it together.