> Most of the stuff from the ancient would is quite easy to reproduce--throw hordes of people at it. The ancient world didn't have some fantastically superior knowledge.

I don't find this type of explanation convincing at all. If your claim was true, then just look at the fact that we still can't reproduce such structures today. I would allege the type of sentiment and thinking your paragraph is representing borders on arrogance. I'm reminded of the story of the illiterate Roman soldier w ho murdered Archimedes and said that man was just drawing circles in the sand.

We are a violent illiterate people who murdered Incan Archimedes and their khippus and since we can't understand their science we try to put down their structures as 'throw hordes of people'.