I've always had a thing about roads, probably because when I was a working archaeologist, I worked for the state department of transportation conducting surveys along them. The only reason we built roads, or at least perfected road-building, however, is because we invented wheeled vehicles.
Assyrian King Hunting Lions. Reproduced from Morey's 1908 Outlines of Greek History
The history of wheeled vehicles begins about 5500 years ago, someplace in northern Europe or southwest Asia. Once invented, the idea appears to have spread like crazy: an alternative explanation is that putting wheels on a wooden box was invented several times in several different places. I figure it doesn't really matter: but the evidence is pretty clear, including some 5500 year old cart ruts in the site of Flintbek.