"The Persians are not warlike. They fight with bows and short spear and go into battle wearing trousers, and hats on their heads.”
Herodotus
The word trouser came into the English language early in the 17th century. It derives from an earlier form trouse or the plural trouzes which first appeared a century earlier. These words are traced back to the Middle Irish triubhas which meant close-fitting shorts. They have been referred to in different ways and gone through many iterations, but the basic trouser as a garment worn below the waist and covering both legs separately has a long history that stretches back millennia.
The oldest pair of trousers has been uncovered at the Yanghai tombs in northwestern China. The material of the pants has been dated back to almost 3,300 years ago. The pants are straight-legged with a reinforced crotch. Bands of decorative patterns adorn the legs. Rather than crafted from large pieces of fabric, these trousers are of wool and woven in precise segments to fit together to make the final garment. It is clear that this garment was made specifically for horseback riding. They help support the hypothesis that the development of trousers paralleled the domestication of the horse. The exact origin of pants is not known, but it is speculated that they probably were first worn by those in wetter and colder climes before being adopted by the nomads of the Central Asian steppes.
Pants provided comfort, warmth, protection, and freedom of movement essential for highly mobile nomadic societies. The concept radiated out from the steppes westward to other ancient cultures. The Scythians, the Persians, the Celts, and the various Germanic tribes all wore versions of trousers. Many of these were warrior societies as well and fought on horseback. Since in some of these cultures, like the Scythians, both men and women were warriors, both sexes are known to have worn trousers.
The Greeks, who had a penchant for inflating their own status as the most civilized society, had a dim view of trousers. Pants, trousers, leggings, these were the hallmarks of barbarians in the opinion of the Greeks. The Greeks used the word thulakos, meaning "sacks", to describe the pants worn by the Persians and other Eastern cultures. The Greeks themselves wore wrapped garments called chitons. These could be long or short and could be draped and fastened with brooches or belts. The Romans, who considered the Greeks the pinnacle of civilization, actively emulated many aspects of Greek culture. Their wrapped garment was the toga, and the Romans shared the Greek disdain for anything that resembled a pair of pants.
The Romans, though, were practical people. Those living along the frontier, first in the military and then civilians, began adopting the dress of the local populations. This included the wearing of trousers. Two types of trousers saw widespread use within the Roman Empire. The first was called feminalia. This was a tight-fitting garment that was either knee-length or down to the mid-calf. The other type was called braccae. These were loose-fitting garments that were closed at the ankle. Both types were originally adopted from the Gauls but were worn by many of the Germanic tribes as well as versions worn by the Persians.
By late antiquity, trousers became a more acceptable fashion. Men started to wear them more often underneath tunics and other similar garments. Throughout the Medieval period, trousers went through a progression of styles and lengths. There was a significant variation across geography and social class. By the 14th century, at least among the upper classes, trousers transformed into what we would call leggings, tights, stockings, or hose. These would often be attached to upper garments such as shirts or doublets, and they would have enclosed feet. As men's hemlines rose by the end of the 15th century, more of the hose was exposed. During this time, respectable women would not be caught in a pair of trousers, pants, or hose. This trend would not be reversed until late in the 19th century when women began insisting on wearing pants again.
By the time the word trouser was making an appearance in the English lexicon, breeches were coming into vogue. These were the heirs to the Roman braccae. During the 17th and 18th centuries, they were the mainstay of men's fashion. Unlike their Roman forbearers, the breeches of this time period often ended at the knee or at mid-calf. Trousers as we know them would be introduced at the start of the 19th century by the style icon Beau Brummell.
George Bryan Brummell - better known as Beau - gained notoriety during the Regency period of England. Not a man of great wealth, he still managed to become close friends with the future King George IV. Because he was not an extremely wealthy man, Brummell decided to go against the conventional style. He simplified his style by eschewing gaudy embellishments and jewelry. He advocated for a more tailored look. He rejected breeches and stockings and favored full-length trousers with a matching or contrasting jacket. This would be the forerunner of the modern suit. King George IV was highly influenced by Brummell's style, and in turn, Brummell changed the course of fashion within English society.
It was still frowned upon for women to wear pants, but this would start to change by the end of the 1800s. Women, who were beginning to engage in more activities, would don pants underneath their skirts to go bicycle riding or to participate in athletics. French designer Paul Poiret, in 1913, became one of the first to create pants specifically for women. He introduced loose-fitting, wide-legged trousers which were to be called harem pants. Poiret was inspired by the tales of the Arabian nights. Movie actresses such as Marlene Deitrich and Katherine Hepburn became trendsetters in the wearing of pantsuits.
For a long time, pants were an essential part of the working-class attire. Trousers were made of sturdy materials such as canvas, leather, and denim. Denim jeans quickly became symbolic of the cowboy, the laborer, the factory worker. During WWI and WWII, women had to step in and take up the roles of the men. This meant dressing the part. More women began wearing pants, trousers, and jeans as part of being in the workforce. Over time, it has become more and more acceptable for women to wear pants. It has also become one of the metaphors in the fight for gender equality.
Here in the United States, we use pants as a generic term for a garment worn below the waist and covering each leg separately. The word pants, itself is derived from pantaloons which is the Anglicized form of Pantalone, a stock character in the Italian commedia dell'arte of the 16th through 18th centuries. The character was often dressed in garments similar to breeches or long trousers. We tend to use the word trouser for more formal wear. In Great Britain, they still use the word trouser. The term pants is reserved for what we, in the States, would call underpants or underwear. So be careful what you say in England.
Further Reading:
A History of Trousers and Pants in Western Culture: Dolores Monet
Why We Wear Pants: Live Science
Who Wears the Trousers? The History, Politics, and Culture of Trousers: Alice Parkin (Oxbow Books)
First Pants Worn by Horse Riders 3,000 Years Ago: Bruce Bower (Science News)