Yeah, but how much was built in the 7th century? And while some technology was relatively advanced at points in the Middle Ages, an overwhelming amount of learning was lost.
I am not sure technology was lost. I haven't seen Notre Dame, but have seen the cathedral in Cologne. They were just using old technology to build a new type of thing. That's why these things are so "clunky" on the outside. It had to be that way to make them open and beautiful on the inside. What wasn't happening was development of new tools, ideas and materials. Progress was very slow, if at all. It took the Enlightenment and climbing out from under Rome to push progress. Something we all don't want to happen again and something that could very well happen under a Fundamentalist Theocracy.