On: The last Incan suspension bridge is made entirely ...

[aarondf]

But how did they string the bridge across the first time?

[jlgreco → aarondf]

Start by pulling across a string (with an arrow, or by climbing over to the other side with it). Use that string to pull over a cord, use that cord to pull over a rope, use that rope to pull over a bridge.

[chiph → jlgreco]

Modern suspension bridges are started that same exact way.