The Wheel

A Roda - The Wheel 
http://encyclopedia.thefreedictionary.com/wheel

A depiction of an onager-drawn cart on the Sumerian "battle standard of Ur" (circa 2500 BCE) Perhaps the most important invention in history, the wheel was—and remains—essential to the development of human civilization. The first wheels appeared in the 4th millennium BCE and were solid wooden disks. Spoked wheels were developed about 1,000 years later in Asia Minor and were used in the chariots of Caucasian horse cultures, which then penetrated into the Greek peninsula and laid the foundation for classical Greece. The spoked wheel remained in use without major modifications until when? More...