Marilyn Monroe was unquestionably a style icon, but what makes her interesting is that her influence went beyond simply wearing beautiful clothes. She helped create a visual language of American glamour that is still being copied more than six decades after her death. The important distinction is that Marilyn's style was partly created for her and partly created by her. The mistake is to think Marilyn's style consisted entirely of gowns and cleavage.
While polo matches were high-society staples in mid-century Hollywood—frequently held at places like the Will Rogers Polo Club in Pacific Palisades or the Riviera Country Club—Marilyn Monroe was not part of that circuit. A few common points of confusion often lead people to associate Monroe with polo or similar sporting events. She did have some scenes with horses over the years (her choice of footwear makes it obvious that this was not a familiar hobby). However, Monroe was famously a regular guest at The Beverly Hills Hotel (living in Bungalow 1 and Bungalow 7 at different points) and frequently spent time in its iconic Polo Lounge, which features classic equestrian polo imagery. So, my imagination is left wondering what she would have worn to a polo match. Surely something timeless and classic like the capri outfit below, but less than the formal gowns that she was famously and fabulously often photographed wearing.
One of her most famous cinematic lines about polo comes from a scene aboard a borrowed yacht in Some Like It Hot (1959), when her character, Sugar Kane, talks with Tony Curtis (whose character was trying to impress her and was impersonating a Shell Oil heir):
Sugar: "Water polo! Isn't that terribly dangerous?"
Junior: "I'll say. Two ponies drowned under me only last week."
Monroe did work extensively around horses in John Huston's Western drama The Misfits (1961), however her footwear in the shot above leaves something to be desired, or shows a real level of comfort around horses (which she didn't reportedly have before the film.)
Photos from Marilyn Monroe: A Life in 100 Takes (also published as I Wanna Be Loved By You) which is a biography by author Andrew Wilson that tells the iconic star's story through 100 focused snapshots. The captions by Wilson for the photos are shocking and reveals an insight into her real life.

