I still find that a little mind-boggling, that in, say, pre-Colombian Mexico, they had wheeled children's toys, and nobody thought to scale that up and build a

I still find that a little mind-boggling, that in, say, pre-Colombian Mexico, they had wheeled children's toys, and nobody thought to scale that up and build a wheelbarrow or a two-wheel dogcart. I mean, they must have been using rollers on some level to maneuver the massive pieces of stone that they used in construction.