Gender Roles

Theda Bara plays Cleopatra here in the 1917 film, Cleopatra. Cleopatra is an example of the Vamp character. Vamping, as in being a sexy outsider, like the flappers, was very popular in the 20s.
Marie Doro played Oliver Twist in 1916 at age 34. She was afforded much more freedom on screen than off
Marie Doro played the male role of Oliver Twist in 1916. It wasn't uncommon for females to play males. However, it was becoming less accepted, as we can see from the snarky town of this article. While Doro wore trousers in the film, it was frowned upon for women to wear trousers in public.
Marie Eline, the Thanhouser Kid, played many male and female roles in early cinema.
Marguerite Clark played both the prince and the pauper in the 1915 film Prince and the Pauper. This demonstrates, further, that while men and women had very separate gender roles and dress in society, it was acceptable for women to play men in the early days of cinema, as they did in the theater. Clark was one of the biggest stars of the day.

Cinema offered an opportunity for women to play roles radically different from those they were allowed to play in society. As Charlotte Perkins Gilman, a prolific writer in the early twentieth century who studied fashion and sociology, noted, the primary function of clothing is to stop society from ever forgetting gender. Gender roles were so strict that women weren't allowed to wear pants. That makes it ironic that in cinema, society did not find it objectionable for women to play boys and men. The public also did not object to women wearing revealing clothing on the screen, which would have been forbidden in regular life.

Gilman, Charlotte Perkins, et al. The Dress of Women: A Critical Introduction to the Symbolism and Sociology of Clothing. Greenwood Press, 2002.