Modern road isn't just asphalt and rock, there are layers of different rock and dirt packed down to provide a solid structure for it to sit on. Asphalt doesn't have bend strength, it's really just holding everything together.
Where is the layer of nougat?
I went and saw the remains of George Washingtons house and it was buried like 10-15 feet underground. All the signs were talking about wars and stuff but not where the tons and tons of dirt came from.
The medieval road looks like concrete, but I would have expected it to be just a mud track.
Concrete itself is roman era, tons of it in Roman ruins if you know where to look.
I think a mud track with occasional bits of gravel is basically what the display is suggesting, it's just that the mud is dry.
It very gentle to walk on with their tentacles.