《重庆卷》 c almost every machine with moving parts has wheels, yet no one knows exactly when the first wheel was invented or what it was used for. we do know, however, that they existed over 5,500 years ago in ancient asia. the oldest known transport wheel was discovered in 2002 in slovenia. it is over 5,100 years old. evidence suggests that wheels for transport didn't become popular for a while, though. this could be because animals did a perfectly good job of carrying farming tools and humans a
