The Evolution of Cartwheels

Part 1 :: The Evolution of Disc Wheels

Part 2 | Part 3

At the end of the Neolithic period, saws were not yet available and to hew a solid wheel from a hardwood tree, would have taken many, many hours. A cleft plank which includes the very centre of the trunk, the site of the original pith, is never favoured today because the centre is always more liable to rot and cause planks to twist badly. This would prevent the single piece wheel from occupying the largest diameter of the trunk, and tripartite wheels seem to have arisen very quickly to replace them, though not before a dowel-joint was invented. Once accurate holes could be drilled, they were simplicity itself.

A selection of tripartite wheels of increasing sophistication is shown below. All use internal dowels to locate the three pieces, and reinforcing staves at right-angles to the main grain to hold them in one plane. From the beginning the locking nature of dove-tail slides was appreciated. At first the two staves were on opposite sides; later, on the same side. Eventually the staves were driven into a curved slot further to increase their rigidity, because, once sprung into position they would not work loose.

Then followed "fenestration"; cutting out holes where the structure allowed, in order to decrease the weight, and then the staves were replaced by "cross-bars" which ran right through the three wheel parts from side to side. This last type with inserted naves remained widespread in the Mediterranean long after spoked wheels had been developed. There is a bipartite wheel shown in a very early picture on a Hittite vase, which is held together with pegged "H" shaped pieces. The axle must always have tended to open up the centre of the wheel by pushing the two sections apart. Four of these "H" pieces, however, in the wheel also shown, constitute a very strong linkage for the parts of a tripartite wheel.

Both these examples also have inserted naves, which were made by boring out the centre of a small log of harder wood and inserting it into a larger hole cut in the centre of the wheel. This meant that the wheel could rotate freely on the axle, and there was less wear when the bearing surfaces were all, side-grain to side-grain. Certainly the end grain of the disc wheel itself, would cut into the side-grain of the axle. The hardwood nave had the further advantage that it was replaceable and as it was gradually increased in diameter, it eventually became the anchorage for the spokes.

A variety of such wheels carried all the loads which were too heavy for pack-animals for at least two millennia. Agriculture on the farm required little transport, as animals for the market walked there on their own feet. It was the City States which created the need to move goods in any bulk or weight, and these in Mesopotamia, Egypt and later in Greece and the other areas of civilisation springing up around the Mediterranean Sea, were all associated with water-born transport. Apart from the exceptional carriage of building stone, the journeys were local and within the capabilities of oxen.

Even military wheeled transport was minimal, the armies starting out initially by sea, living off the land and making any "engines" of war from local materials. However there must have been some ox-wains to carry the personal effects of the leaders, and there are records of these having been used as chariots to provide headquarters command posts in battle. Clearly they did not move at great enough speeds to be used as fighting vehicles.

No further progress occurred until horses, ridden at first only by important leaders became more generally available and were used to pull the chariots. The Roman Legions were so large and numerous, and their campaigns so sustained, that considerable baggage trains would be required to provision their ordnance.

Next >>