"I've heard that we still don't know how they produced the dome, another nonreinforced wunder construction that's survived for millenia." We didn't, but we do

"I've heard that we still don't know how they produced the dome, another nonreinforced wunder construction that's survived for millenia." We didn't, but we do now. It has recently been fully understood to have been volcanic ash mixed into the concrete that makes it so strong and stable. https://en.wikipedia.org/wiki/Roman_concrete https://en.wikipedia.org/wiki/Roman_concrete http://www.romanconcrete.com/docs/spillway/spillway.htm http://www.romanconcrete.com/docs/spillway/spillway.htm