Why these Hollywood dresses are worth millions

A series of costumes from The Sound of Music made $1.3m at an auction on Sunday.

Much of that figure can be attributed to the fact that Julie Andrews' dress from the famous "Do-Re-Mi" song was among the offerings.

The sale is the latest in a long line of stunning auction performances for outfits worn by classic cinema's leading ladies.

In 2011, for example, the dress Marilyn Monroe wore above a breezy New York grate in The Seven Year Itch sold for $5.6m, while Audrey Hepburn's "Ascot" dress from My Fair Lady made $4.6m at the same Debbie Reynolds Collection auction.

When it comes to movie memorabilia, dresses are at the top of the tree. The reason?

Over to film expert Sir Christopher Frayling, who recently curated the V&A's Hollywood Costume exhibition in London.

In an interview with Paul Fraser Collectibles he explained that the attraction of Monroe's and Hepburn's two dresses to collectors is a combination of the famous leading ladies who besported themselves in them, and the iconic nature of the scenes.

"It's a mixture of the women who wore them, and the moments in the film that people want to remember. The updraft from the subway, and in the case of Audrey Hepburn, leaning over during the race and getting over excited," Sir Christopher explained.

When you apply these thoughts to The Sound of Music dress, all becomes clear. Julie Andrews, while perhaps not quite in the same "screen-siren" league of a Monroe or a Hepburn, is hugely famous around the world, primarily for her starring roles in The Sound of Music, and Mary Poppins.

And then there is the mountaintop scene in which the dress features, where Maria teaches the Von Trapp children to sing. It is among the most memorable scenes in cinema, helped by its wonderfully catchy and clever Rodgers and Hammerstein "Do-Re-Mi".

So we know what to look for, but unfortunately dresses from iconic scenes do not come up for sale everyday. Here's the one I'm waiting to appear:

Tippi Hedren's green dress from The Birds. That auction will be a big one.