Artist's commentary
Shōdō Shōnin (Saint Shōdō, roughly) was blocked and troubled by the rapid stream when Jinja-ou (Lord of the Deep Sands) showed up. Jinja-ou then summoned his snakes and turned them into a bridge, and the bridge disappeared after Shōdō Shōnin crossed. That's how the legend goes, it seems.
The rustic bridge constructed here is called "Sedge Snake Bridge", and it seems like it was the origin of the sacred bridge.
So far, it seems it has been rebuilt many times.