Rufus T. Firefly wrote:HONDO74 wrote:It would be interesting to see a picture of a bridge like that under construction. What method did they use to keep all the rocks from coming loose..
It's all, at least on the exterior, cut stone fitted together and mortared/cemented in place. From photos that I've seen in the past, lots of scaffolding, rigging, and framing was used to assemble the arches. Might be one of those art forms that we are rapidly losing........
As we all know, such arches were invented by Ancient Rome, especially evident in their viaducts. However, Roman arches would often have a "Keystone" put in place as the final phase of construction, at the highest point in the middle of the arch. The keystone's presence determines that mortar/cement (also invented by the Romans) isn't necessarily needed, with each stone constructing the two arched sides putting the pressure of their weight against the Keystone, holding it all up together. Using some type of mortar would make the structure all the more stable and robust. Of course, since far more than a simple aqueduct arch, built to transport a simple narrow trough of water, is in the Mt. Union, PA bridge widened to hold a wide roadway, the scaffolding, rigging, etc. were part of the construction process, as you said, as it was in ancient times. (Do I see something of a keystone in that far right arch?)