Riding Horses
Many experts believe that the earliest horses were too small to carry riders (around 12-14 hands). Constrast this with a modern draft horse, which is around 17 hands. Essentially, these were ponies. There is some dissent about this point, and some people seem to think this silly, as people even today ride ponies that are that size.
On this, Amy Smith writes: '(by the way, 12-14 hand "ponies" would have no problem carrying adults, provided they were of the sturdy native stock available before the overproliferations of "breeding"

As my last summer's brief experience among yak herders on the tibetan plateau indicated... their "horses" of that size would carry a full-grown men plus two big sacks of barley flour or a bag of cheeses... this at 11,000 ft.)'
XXX maybe all horses didn't start out small? Lisa to supply reference.
Around 4000 BCE seems to be when horse riding first started to take off. Archaeologists have found evidence of early bridles in Eastern Europe, southern Russia. Antler cheekpieces and toggles for soft mouthpieces were found north of the Black Sea. Horse teeth have been excavated in the Ukraine with possible evidence of bit wear.
In 3000 BCE, the horse was domesticated in Ukraine, northern Caucasus, central Russia and Kazakhstan. This was made possible in these regions because the new system of cultivation meant that food was at a surplus, and horses could be used for other purposes.
Horse riding seemed to take off much more slowly in the Near East. It is still a mystery as to the exact reason, although in a letter to King Zimri Lim (1782-1759 BCE), the king was told that riding on chariot or mule is ok, while riding on horseback was bad. Big mystery, mostly. A horse historian named Mary Littauer opines that horse sweat was considered too gross to ride directly upon the beast.
In 1500 BCE, entirely metal bits were being used in Near East, including a new form of bit: the snaffle bit. This bit offers more control of the horse. It places pressure on the corners of the horse's mouth, rather than center. Some of these bits are jointed, while some are simply a solid bar.
From 1000 to 509 BCE lived a race of people known as the Etruscan Horsemen, whose entire lives revolved around horses. Unfortunately, the Romans destroyed all written records of these mysterious people, although a rich legacy of artwork remains.
The earlist horsehoes made by Romans, called 'hipposandals', and were tied on with leather. They were extremely heavy.
Around 800 BCE, another nomadic horse culture known as the Scythians arose. A number of Russian Steppe tribes conglomerated into a single nomadic horse people and invaded Near East. They featured composite bowfire from horseback, and were quite effective in battle. They performed the first recorded geldings, their wealth was measured in horses. They were obsessed with their horses, to the point of bringing horses to their graves, and decorating their tombs with fancy gold horse-centric artwork. They also, randomly, were the earliest recorded wearers of trousers.