I was wondering exactly why you found it impressive that Plato thought up the Allegory of the Cave so long ago. Obviously he was rather intelligent for any time, but that kind of thought seems to be rather basic, in that it doesn't build off of other thoughts or theories. It takes a great mind to come up with it, but it would be just as impressive if it had been thought up in Ancient Greece or yesterday.

Perhaps it would be just as amazing now, but then again, I feel the time period does add a little bit to the impressiveness.  For instance, back then most people thought lightning occurred because the gods were fighting.  Today, we are much more educated and have access to much more general knowledge.  As a result, you would expect this to leave people with more time to think about greater things such as the ideas in The Allegory of the Cave.  Plato is impressive because he thought of it amidst a very unknowledgeable people.