Quote Originally Posted by Rudeofus View Post
PS: that's stone, not concrete. They had no concrete when that theater was built
You may be surprised to hear it, but at least the Romans DID have concrete. Just not reinforced with steel wire. It is one of the things that made the marvelous Pantheon dome possible, and many, many other buildings. In fact, many Roman structures, even looking as build from bricks, contain some interior concrete reinforcement.

Their invention went lost though during the dark middle ages here in Europe.

Here is site dedicated to Roman concrete: