Cribs - What Are They All About?

I just finished round three of trying to get my baby to nap in the crib. Since she's started crawling, I'll hear her wake up and run in to find her flipped over onto all floors happily crawling around the bed. I've been propping pillows all around her to keep her in the middle but, as of yesterday, these are just more obstacles she's learned to overcome! I've decided our mattress is going on the floor but until my hubby gets home tomorrow to move the bed, I've decided the crib is the safest. Oh the crib... Who invented the crib? I mean really, what is the history of the crib? And at what point did we, as a species, go from sleeping on a dirt floor together as a family, to deciding this is dangerous practice and babies need to be in their own beds (in their own rooms nonetheless) or we'll risk rolling over them? I understand that our society has come a long way from sleeping on the ground and have moved into big beds with comfy mattresses but, what about the little babies? They don't understand why they are being separated from their mothers (or main caregiver) to sleep. One day, when I get time, I'm going to do a little research on where cribs came from. Cribs... So interesting.