One of man's simplest but most important inventions. A Sumerian (Erech) pictograph, dated about 3500 BC, shows a sledge equipped with wheels. It is also shown in Uruk pictographs, c 3400 BC, and on the Royal Standard of Ur. Early wheels were solid and unwieldy, made of a single piece of wood or three carved planks clamped together by transverse struts. Spoked wheels appeared about 2000 BC, when they were in use on chariots in Asia Minor. The wheel was not used in pre-Columbian America, except in Mexico, where small pull-along toys in the form of animals were made in terra-cotta. The use of a wheel (turntable) for pottery had also developed in Mesopotamia by 3500 BC.