Ancient Mexico built wheeled toys but never a wheeled cart
Archaeologists in Mexico have dug up small wheeled figures, apparently children's toys, some around 3,500 years old. Yet Mesoamerica never put the wheel to practical work before the 16th century: no carts, no wheelbarrows, not even a potter's wheel. One leading explanation is that the Americas had no large animals able to pull a wagon.
The candidates were poor. The American bison, nearest local relative of cattle, resists domestication and was never tamed; native horse species had died out roughly 12,000 years ago; and the llama, the only big animal domesticated in the hemisphere, carries packs but is built wrong for hauling and had spread little beyond the Andes by the time Europeans arrived. Some scholars suspect the toys' wheels began as spindle whorls, the discs used in spinning thread.
Elsewhere the wheel grew out of rolling heavy loads on logs. Solid wooden discs with an axle hole appeared in the Copper Age, between about 4500 and 3300 BCE, and slices cut straight across a trunk made weaker wheels than ones assembled from shaped boards. Miniature clay wheels north of the Black Sea predate 4000 BCE, and a potter's wheel from Ukraine's Cucuteni–Trypillia culture is older than any in Mesopotamia. Spoked wheels, lighter and faster, appear with the Sintashta culture around 2000 BCE, and Celtic chariot builders added iron rims in the 1st millennium BCE. In 2016 a wheel about a metre across, with its hub, turned up at Must Farm in East Anglia, dated to 1100 to 800 BCE.
Why bother with wheels at all? Drag a 100 kilogram load 10 metres with a friction coefficient of 0.5 and it takes about 4,905 joules. Mount it on four wheels a metre across, with 50 millimetre axles, and the rubbing happens only in the bearings, which slide just half a metre; the work drops to roughly 123 joules, a fortieth as much.
Spoked wheels stayed largely unchanged until the 1870s brought wire spokes, which work in tension to stay stiff yet light, and pneumatic tyres. The English word traces back through Old English hweol to a root meaning to revolve, sharing ancestry with Greek kuklos and Sanskrit chakra.
Source: Wheel
