When the wheel was adapted to improve transportation with carts and wagons, the process fomented and encouraged the construction of Roads to make the new vehicles more useful, and to speed up transportation between an empire’s cities.
The wheel is an ancient invention. It was first used, as far as we know, around 6300 BC by the Sumerians. And wheeled carts were in general use throughout the Middle East by 3500 BC. The four-wheeled, two-axle wagon was being used by 2500 BC, usually drawn by oxen. Wheel technology by 2400 BC produced the chariot, a light vehicle using wheels with spokes and metal tires, which could be drawn at high speeds by teams of horses or the wild ass of Asia, the onager. Wheeled vehicles made land transportation much more efficient, since a team of two horses could pull a wagon weighing several tons while two pack horses could not carry more than a quarter ton between them. The downside was that wheeled vehicles required roads, and to move fast and far with heavy loads they needed well-made and well-maintained roads which, after irrigation systems, became some of the first great construction projects undertaken by governments. Although the Roman roads system is the most famous in the ancient world, the Persian Empire had a Royal Road that stretched over 1500 miles from Sardis in Asia Minor to Susa near the coast of the Indian Ocean.