An international group of archaeologists have found these trousers—worn between 3,000 and 3,300 years ago—in a tomb in western China. The trousers were invented for horse riding by Chinese pastoralists and are the oldest known examples of this kind of apparel:
"This new paper definitely supports the idea that trousers were invented for horse riding by mobile pastoralists, and that trousers were brought to the Tarim Basin by horse-riding peoples," remarks linguist and China authority Victor Mair of the University of Pennsylvania.
Previously, Europeans and Asians wore gowns, robes, tunics, togas or—as observed on the 5,300-year-old body of Ötzi the Iceman—a three-piece combination of loincloth and individual leggings.
According to the The History Blog this is how they made it:
The trousers are formed from three separately woven pieces: two straight-cut legs and a stepped cross-shaped crotch that covers the genitals from the front to the back. There are side slits in the waistband, and a remnant of string at the edges of the slits suggests the trousers were closed on both sides with drawstrings.