Clark, the workmanship on this has to be seen to be appreciated. The hand craftsmanship is everywhere.
Tony, It looks like some sort of scaffold where you climb down that ladder but it looks very old. There is some sort of foam looking sealer on the roof of the arch that didn't photo well.
Any idea what the steel beams and boards underneath the bridge are for Steve? Looks like they have either done work on it at some time and left their stuff there...or some kids have a fort under there, lol.
The chisel marks (in photo 8) distinguish these older structures from modern ones. I can't look at a UCEB and see any connection with the humans involved in making it. This bridge shows the marks left by a hand how many generations ago.