The chariot, at least in the West, is more closely associated with the Ancient Egyptian civilization than any other - though the design appeared in varying forms with a variety of armies throughout history. In concept, the chariot design was always similar - it represented a light, fast-moving battlefield component to any army. Its direct use on the battlefield, however, could be customized as needed.
The Sumerian chariot was an amalgam of Egyptian and Hittite chariot production techniques. The resulting design was quite unique, utilizing four horses over the traditional two in the Egyptian way and taking on a full series of four wheels as opposed to two. The Hittite influence brought about the armored cab where the driver and additional soldier(s) stood. The Sumerian chariot was reportedly as least an equal to the ferocious Egyptian design.
The chariot has also appeared as far east as the ancient Chinese dynasties, with the arrival of the chariot attributed to the Indo-European regions as an origin. The chariot in Chinese culture was one of high stature due to the high cost of obtaining horses to pull the cab. The Chinese chariot was designed to carry three men into battle as opposed to the traditional two and included the warrior (who could dismount the cab to fight or fire arrows from it), the driver (controlling two or more horses) and a servant to the warrior (replenishing his master's arrow supply and generally doing what needed to be done to keep his master alive in battle).
The top speed of the ancient chariot centered around the type of equine used to pull the cab and the general construction of the cab and wheels itself. Some civilizations used donkeys whilst others used specially bred thoroughbreds and taking the concept further, some chariots could be pulled by as many as four equines and as little as one. Cab design also varied from civilization and era where some were shown with complex axle designs, stability features, armor usage and the use of four wheels instead of the traditional two. In a more ferocious form, the scythed chariot appeared armed with large blades on the wheel hubs and can assemblies. The blades were designed to slice through standing men with ease and leaves only the imagination as to the carnage these devices could have achieved on the battlefield. Of course this development could be two-sided as any scythed chariot unit running amok could easily run back into friendly lines, causing equal decimation to their own friendly ranks.
Though initially viewed as an instrumental weapon of terror at the forefront of any advancing army, modern belief of the chariot as a battlefield instrument has the chariot as more of a "clean up" weapon used to decimate routing enemy. In ancient times, most casualties - it is believed - occurred when one army made the terrible decision to run from the battle as this was the moment that their pursuers could wreak havoc on the confused lines in retreat.