(CNN) - Natalie Portman said experiencing "sexual terrorism" at the age of 13 made her feel the need to cover her body and inhibit expression.
The award-winning actress shared her traumatic experience Saturday while addressing a crowd of thousands gathered in downtown Los Angeles for the Women's March.
Portman remembered turning 12 on the set of "Léon: The Professional." It was her first film. She played a young girl who befriended a hit man in hopes of avenging the murder of her parents, she said.
A year later, when the movie was released, she opened her first fan letter. It was a "rape fantasy" from a man.
"A countdown was started on my local radio show to my 18th birthday -- euphemistically the date that I would be legal to sleep with," she said. "Movie reviewers talked about my budding breasts in reviews. I understood very quickly, even as a 13-year-old, that if I were to express myself sexually I would feel unsafe and that men would feel entitled to discuss and objectify my body to my great discomfort."
Portman said she adjusted her behavior, rejected roles with kissing scenes and emphasized her "bookish and serious" side. She built a reputation as a "prudish, conservative, nerdy, serious" young woman in order to feel her body was safe and her voice heard.
"At 13 years old, the message from our culture was clear to me," she said. "I felt the need to cover my body and to inhibit my expression and my work in order to send my own message to the world that I'm someone worthy of safety and respect. The response to my expression, from small comments about my body to more threatening deliberate statements, served to control my behavior through an environment of sexual terrorism."