Astonishingly recently as a transport improvement, perhaps too recently to say if it'll really catch on. The first evidence is dated to western Eurasia around 5500 years ago, with depictions in eastern Europe (Poland, Slovenia and Ukraine) and Mesopotamia: it's unclear which came first, but judging by its appearance in so many places in a short period its usefulness can be imagined to have been recognised early. The first wheels were solid, spoked wheels appearing a millennium or so later. The potter's wheel is conventionally assumed to have come rather earlier, though in the same period.

https://traveltoeat.com/chariots-the-first-wheels-of-war/ offers a wealth of images and http://www.ancient-origins.net/ancient-technology/revolutionary-invention-wheel-001713 discusses some technical aspects: the world's great museums seem to have fallen asleep on the job when the topic would seem an excellent opportunity for collaboration and promotion.