Ancient Technology: how is this possible?

I have been doing some reading, and was wondering how many Ancient cultures have some examples of technology that would be deemed impossible to make if they were as stupid as we thought. How is this possible if humans were stupid at the beginning? http://www.cracked.com/article_21686_5-awesome-technologies-created-by-ancient-civilizations.html http://listverse.com/2013/04/12/10-mysteries-that-hint-at-forgotten-advanced-civilizations/