Women were expected to ride horses sitting aside rather than astride the horse as far back as can be remembered. There is evidence of this on ancient Greek vases, sculptures, and Celtic stones.
Since it is only possible to control a horse by riding it astride, it was decreed that side-riding is the right, modest way for a woman to be transported from place to place.
Early sidesaddles were but a seat mounted behind the man’s saddle, enabling the woman to be relatively comfortable hugging the rider’s back, or while a male person would walk leading her horse.
Common knowledge had it, that the woman who would ride a horse astride would lose her virginity. Yet, married women were also expected to ride on sidesaddles.
Unsurprisingly, it was women who invented the sidesaddle that enabled them to actually control their horses, by adding ‘horns’ that allowed them, modestly, under the cover of the long skirts, to grip the saddle with their thighs.
These were Anne of Bohemia (1366–1394) and later Catherine de' Medici (1547–1559).
We owe much to nonconformist, brave women such as Diane de Poitiers (1499–1566, mistress to Henry II of France,) Marie Antoinette (1755–1793) and Catherine the Great of Russia (1729–1796), who defied conventions and rode astride, most likely because they were riding other powerful horses: their male lovers/husbands.