Why is the lower part of ancient men's wear like a skirt?

The reason why the lower part of ancient men's clothing was like a skirt was because there were no underwear and trousers at that time, and men only wore skirts, which was called petticoats. In ancient times, clothes were separated, with the upper part being clothes and the lower part being skirts. Although the clothes are wide, they are easy to be exposed if they are too big or don't obey the etiquette, so a set of etiquette system based on kneeling has been formed.