|Damascus Steel Blades|
So the fact that our predecessors knew how to do some things that we still haven't figured out shouldn't be too surprising.
That's not to say that the Egyptians had space travel, or the Mayans could predict the future. It just means we haven't recovered the processes by which they made things like Greek fire, layered stained glass and Damascus steel. (Of course, napalm does make Greek fire seem a little old hat.)
And for the really impressive pre-industrial stuff, check out guys like Heron of Alexandria.