The wheel and the Bronze Age

The oldest wooden wheel yet found, about 5,200 years old, came out of a marsh in Slovenia in 2002.

The wheel came late

It sounds backwards, but farming, towns and even temples came before wheeled vehicles. Potters’ turning wheels were already old technology when carts and wagons began to appear, around the middle of the 4th millennium BCE, over a wide area from Mesopotamia to central and northern Europe, almost at the same time. The earliest well-dated picture of a wagon, with four wheels and two axles, is scratched on a clay pot from Bronocice in Poland, from about 3500 BCE. In Mesopotamia, clear pictures of wheeled vehicles come later.

The oldest wooden wheel

In 2002 archaeologists working in the Ljubljana Marshes, about 20 kilometres south of the Slovenian capital, found a wooden wheel together with its axle. Radiocarbon dating gave an age of about 5,100 to 5,350 years, roughly 3350 to 3100 BCE, which makes it the oldest wooden wheel yet discovered. It is about 70 centimetres across and made of two ash planks joined together; the axle is oak. The axle has a square end that fitted a square hole in the wheel, so wheel and axle turned together, like the wheels on a toy train.

Why a wheel helps

Dragging a heavy load means the whole load slides against the ground, with a lot of friction. A wheel turns that sliding into rolling where it touches the ground, and the remaining rubbing happens only at the axle, a small surface that can be greased. Early solid wheels made of planks were heavy, and the first wagons were pulled slowly by oxen. The spoked wheel, light enough for fast two-wheeled chariots pulled by horses, came later: the oldest known chariots come from burials of the Sintashta culture in the southern Urals, dated about 1950 to 1880 BCE.

On the Standard of Ur, made around 2550 BCE, rows of shell and stone inlay show four-wheeled battle wagons with solid wheels, each pulled by a team of donkey-like animals.

Copper, then bronze

People first hammered lumps of natural copper and later learned to smelt copper from ore. Pure copper is soft. Adding a little arsenic, or better, tin, makes a harder metal that is also easier to cast: bronze. Bronze melts at about 950 °C, while pure copper melts at about 1085 °C. Tin became the main added metal in the late 3rd millennium BCE; it was safer than arsenic and easier to control. A good mix is about ten parts copper to one part tin.

Tin was rare

Copper ore is fairly common; tin ore is not. Mesopotamia and Egypt had little of either, so bronze depended on long trade routes over land and sea. The Uluburun shipwreck, found by a sponge diver off southern Turkey in 1982 and dated to about 1320 BCE, carried about ten tons of copper ingots and about one ton of tin ingots, enough for about eleven tons of bronze at a ratio of ten to one. It also held glass ingots, elephant ivory and a gold scarab bearing the name of the Egyptian queen Nefertiti.

Stone, bronze, iron

In the early 19th century the Danish museum curator Christian Jürgensen Thomsen sorted his collections into objects of stone, bronze and iron, and this "three-age system" is still used. In the Near East the Bronze Age is usually dated about 3300 to 1200 BCE. Other regions started later: bronze casting reached the Yellow River valley with Erlitou and the Shang, and northern Europe later still. Around 1200 BCE many palace states of the eastern Mediterranean fell, and over the following centuries iron, whose ore is far more common than tin, gradually replaced bronze for tools and weapons.