Wooden or metal disc attached at its central point to an axle or pivot in such a way that it can rotate freely to allow a vehicle or other mechanical device attached to the axle to move freely. Widely regarded as one of the single most important inventions ever made, the idea of a wheel seems to have cropped up in many cultures from early times. However, its application in pre‐industrial societies is mainly confined to agriculturalist and pastoral societies in the Old World. One reason for this is that wheeled vehicles can only be used on relatively flat terrain or along constructed bearing surfaces such as roads and tracks. Another prerequisite is the availability of draught animals to pull wheeled vehicles.
The earliest evidence of wheels comes from Uruk, Iraq, where depictions of what appear to be sledges mounted on four wheels appear on pictograms of the early 4th millennium bc. From the later 4th millennium bc there are a series of depictions of wheeled vehicles on pottery or as ceramic models across a wide swathe from the Near East via central Europe to the Atlantic coastlands: from the TRB Culture in southern Poland, the late Copper Age of Hungary, the Kura–Araxes Culture in Transcaucasia, the Kurgan cultures of southern Russia, and the Corded Ware cultures of northwest Europe. In all cases these wheels appear to be solid wooden discs with a thickened hub. Actual examples of such wheels have been found dating to the mid 3rd millennium bc, for example at De Eese, the Netherlands. Later, multi‐part discs were made, often with three elements secured together with crosspieces on either side.
Spoked wheels appear from the mid 2nd millennium, first in the Transcaucasus region, but soon afterwards within broadly the same areas that already use wheeled vehicles. By the 1st millennium bc iron tyres were being fixed to the outside of the rim of spoked wheels, proving to be a far more robust yet lightweight structure. Wheels were not used indigenously in the Americas or in Africa south of the Sahara.