In Ancient Rome, "knights" initially referred broadly to all cavalrymen, but later came to mean those who could afford to keep horses. This was because, during the early formation of Ancient Rome, warfare between tribes was frequent, and groups of personal retainers dedicated to combat formed around clan chiefs, including cavalrymen.
In the Mediterranean, horses were not used for plowing as they were in Britain. Nor could they produce wool like sheep, or be "specialized" for transport like mules and donkeys.
In short, keeping a horse required a bit of spare money. As time passed, knights became people with a certain amount of property, forming a social class. They ran estates, lent money at usury, sold slaves, contracted tax collection and public works. Unlike nobles, they got personally involved in the work. In any case, they had no intention of entering politics, and later the Senate of the Directory even issued a ban prohibiting senators from engaging in commerce.
In Gaul, Caesar had seen the cavalry of the Germanic king Ariovistus. They numbered six thousand, accompanied by an equal number of infantry. Every one of those infantrymen was agile and skilled. Whenever they needed to march a long distance or retreat swiftly, the trained infantry could react at once. Merely by clutching the horses' manes, they could advance and retreat alongside the cavalry. If a cavalryman was seriously wounded and fell from his horse, the infantry would immediately surround him and form a protective ring.
In 75 BC, while Pompey was fighting in Spain, he reported to the Senate of the Directory that the soldiers had not only suffered heavy losses in the war, but had gained nothing besides worthless spoils. The campaign was fraught with danger, offered little chance of victory, and was hardly glorious. Both generals and soldiers