I believe the Pantheon dome was, not sure about the Parthenon though. But it's definitely very old. A lot older than some people realise I think. But yes, not disagreeing that it can be beautiful. I've seen many beautiful concrete sculptures, but I don't think it's the first thing that springs to mind for many.
The replica in Nashville, TN has concrete in its construction. The original, I believe, is made of marble. (but I'm less certain. I've never seen the real one, sadly.)
You are thinking of the Pantheon. It is a temple in Rome built in the first century, and it has a dome made of concrete. (The Parthenon on the other hand is a temple in the Acropolis in Athens, but not related to concrete)
