The Wheel has been around for several thousand years, but to use it on a wagon requires someway to leave the wheel rotate and carry the load on the wheel.
There are two ways to do this, the first is the method used pre-Dark Age method. You put the wheel physically to an axle, and both wheels and axle rotate. Thus you have to have something strong enough to haul the load and move the wheel but also the axle. AND the axle has to be heavy and strong enough to withstand it rotating underneath whatever load was in the wagon.
The other method is to fix the Axle to the wagon so it does NOT rotate, and then turn the wheel around the axle. This requires even more wear the the above method UNLESS you use ball bearings. The Ball Bearings roll around the axle and the wheel, transferring the weight of the wagon to the Wheel BUT not having excessive wear on the Wheel or the Axle. This is how almost all wheels since the Dark Ages have been made.
The issue is when was this first done? Records in the Dark Ages are even less then in the Greek and Roman periods of History, but we have parts of wheels and wagons that clearly show ball bearings being in wide spread use during that time period. We do NOT have that for the Roman and Greek Periods AND even the periods before the Arab Conquest.
Thus most armies prior to the Dark Ages use Oxen to haul their supplies for Oxen is strong enough to haul huge axles in addition to the Wagon and what ever was in the wagon. Horses were used for only light loads, one to two man Chariots or similar light wagons.
Before the discovery of the Ships on Light Nimi, every one was willing to accept that the Ball Bearings was one of those Dark Ages inventions (Along with the Horse Collar, Horse Shoe and Hay) that made the use of Horses possible for heavy hauling (And plowing, but it is clear that the Heavy Iron Plow was know in Asia Minor at about the time of Hannibal, then was taken to Poland or the Ukraine in the late Roman Period, and once introduced to the Slavs, the Slavs used it to spread throughout Eastern and Central Europe, replacing the pre-existing pasture system of the Ancient Germans and Celts, with a higher population Farming society, moving as far South as Central Greece, to the Elbe River in present day Germany, with one tribe making it to England all during the 600s).
Anyway, the above Horse revolution was centered on the Horse Collar (Which permitted horse to haul heavy loads AND to do plowing), Horse Shoes (Which permitted horse to get traction with heavy loads and while plowing), and hay (Which provided Horse with the Food needed to do the above heavy work and plowing).
Oxen stayed around for when it came to endurance and heavy hauling, oxen still could beat horses. One of the best example of this is during the time of the Oregon Trail. On the Oregon Trail horses/Mule trains would pull out and move faster then oxen wagon trains, but the horses and mules would be worked to death in about two weeks (Thus when Stagecoaches were introduced on the trail, the horse and mules were replaced every 20 or 30 miles so to give the horses/mules a rest). After about two weeks the Wagon Trains used Oxen would pass up the wagon trains using Mules/horses do to the horses/mules dieing of over work. Horse and mules can do heavy work for about two weeks, then need a break, oxen could go on for a long longer time period.
Thus, until the invention of the Steam Locomotive, any army (or any other large movement of people) was restricted to the speed of oxen if they wanted to be in the field for more then two weeks. If an army was careful and save its horses till speed was needed, it was a deadly combo, but if the Army used its Horses to much, the army could find itself without supplies and the ability to move. To a good degree Steam Locomotives ended this dual cycle (Horses being used to haul from rail head to front instead of hauling all the supplies the army needed). What Trains did not do, Trucks did (Even the Russian Army, the most Horse dependent army during WWII, used horses only from supply base to front, instead of the nearest rail head, trucks hauled the supplies from Rail head to the Supply base). Since WWII, horses have been replaced in almost every army. Mules are still used in certain locations (i.e. where trucks can not go, and helicopters can not go do to the fact the other side has air superiority OR the base for the Helicopters are to far away).
I go into how Oxen and Horses were replaced to show you how important Ball Bearings was. It took over 1000 years before you had something as dramatic as ball bearing axles that actually improved land transportation. It is for this reason Historians are amazed at the use of Ball Bearings almost 700-800 years before we have records of them used in transport.
Back to Ball bearings. The Lake Nimi boats had at least one statute that had ball bearings at its base. This permitted the statute to move around using a lot less power then if the Statute had to move its entire base. This is the key to Ball Bearings and why they are so important. How far did this invention go? We do NOT know. Was it a flash that was then forgotten? Was it like the Iron Plow and the Water Wheel, ignored by the Roman Elite and thus NOT spread except by the peasants talking to each other (This is how the Water Wheel is believe to have moved from the Middle East at the start of the Roman Period, but only reached Western Europe by the end of the Roman Period). Was it ignored until someone else saw it and took it home and started a social Revolution (This is how the Heavy Iron Plow is believed to have moved from Asia Minor to the Slavic people, who then used it to convert Central Europe to Farming instead of Pasture).
What else did the Roman's use Ball Bearings for? Clearly not in wagons, but anything else? More data is needed, but we do not have the data from the period in question. Ball Bearings could explain the spread of the Slaves in the 600s, the Slavs spread because they could (Also can explain why the Eastern Roman Empire, after the Arab Conquest, decided the bigger threat was the Slavs moving into the Balkans NOT the Arabs holding Egypt and attacked north not south from Constantinople). Question, Question, Questions, maybe we will find out in the future.
Horse shoes, earliest record is 510 AD (Some records exist prior to that date, but all are questionable).
http://en.wikipedia.org/wiki/HorseshoeThe Horse Collar, came out of China (834 AD and was in Europe by 920 AD):
http://en.wikipedia.org/wiki/Horse_collarThe Heavy plough know in England by 600 AD, but terms for it tends to be Slavic in origin:
http://en.wikipedia.org/wiki/Plough