Sonja

Now that's a well-built bridge!

If it is indeed still roman, which is not really established, it could be unp to almost 2000 years old.
Anyway the story is like this: The emperor had his road to germania built through the valley in a way it usually did not lead through the bottom, due to those valleys being not a very convenient place for a cart and marching road, getting always stuck in the snow, then very soggy and full of alpine native people, not all of them harmless and friendly. So he rather had it cut it into rocks a few metres elevated from wetlands and settled knolls in the side of the big mountains. Perhaps he however only had a wooden bridge across this gully and that arch is from a medieval incarnation of the inn valley road, at least there are some claims it must be so whilst others wrote it was always called the roman bridge so roman it likely is. Anyway it is to old there are propper records. And it had a few drastic renovations in early modern times to safe and improve it so to argue about stuff like cart spur width is also futile.