One Wheel Transport Evolution

• 3300–2200 BCE: Early Bronze Age
• 2200–1550 BCE: Middle Bronze Age, invention of the spoked wheel and the chariot
Wide usage of the wheel was probably delayed because smooth roads were needed for wheels to be effective. Carrying goods on the back would have been the preferred method of transportation over surfaces that contained many obstacles. The lack of developed roads prevented wide adoption of the wheel for transportation until well into the 20th century in less developed areas.
Early wheels were simple wooden disks with a hole for the axle. Because of the structure of wood, a horizontal slice of a tree trunk is not suitable, as it does not have the structural strength to support weight without collapsing; rounded pieces of longitudinal boards are required. The oldest known example of a wooden wheel and its axle were found in 2003 at the Ljubljana Marshes some 20 km south of Ljubljana, the capital of Slovenia. According to the radiocarbon dating, it is between 5,100 and 5,350 years old.