All over Europe, there are monuments of stone such as stonehenge, although many are not so grand as stonehenge is. Contra Asterix, the Celts didn't carve out menhirs and things like that. The stones were already there by the time the Celtic culture came into being.
In medieval times people linked them with Bible stories about the giants that used to roam the earth... says Wikipedia, anyhow.
What did people think about them in ancient, historical times? Did the Romans have any thoughts on who built structures like stonehenge, and for what purpose?