From the introduction
A small bridge has been set up here to cross the river tranquilly flowing along through the forest. While other architects elsewhere would have set up a much simpler wooden bridge elsewhere for such a small dirt path through a forest the architect of this bridge decided otherwise. The regular spring flood would tear away a mere wooden bridge with ease time and again, especially once driftwood gets caught against it.
For this very reason the bridge's builder decided to set up a chain bridge. It's massive stone pillars have withstood every flood so far and although the chains have become rusty they have not broken yet either. Only the wooden planks laid down on the chains have to be replaced every once in a while when the bridge warden is surprised by a flood and has no time to remove them.