Dorothy's $6 million ruby slippers from 'The Wizard of Oz' are the most expensive piece of pop culture ever - but 12 more collectibles came close

Mark McGwire's 70th home run ball: $3 million

In the summer of 1998, baseball fans across the country watched Sammy Sosa and Mark McGwire try to break Roger Maris' single-season home-run record. Eventually, both players broke Maris' record of 61 home runs, which had stood since 1961.

Sosa ended the year with 66 home runs and McGwire hit an even 70. Even though it wasn't the home run that broke the record, comic book millionaire Todd McFarlane purchased McGwire's 70th home run ball for $3 million. He also owns McGwire's 67th, 68th, and 69th, and Sosa's 66th home run balls.

The Cowardly Lion's costume: $3.1 million

The ruby slippers are not the only sought-after costume from "The Wizard of Oz." Dorothy's dress from the movie sold for over $1.5 million, but another character's wear has sold for more.

Actor Bert Lahr donned this costume made of actual lion skin and fur for the 1939 film. He sung "If I Were King of the Forrest" and found his courage in this costume.

Bonhams auctioned off this piece of movie history in 2014 for $3 million.

Honus Wagner T206: $3.1 million

The most famous baseball card of all time is also the most expensive. There is an entire book dedicated to the card and it has arguably overshadowed Wagner's Hall of Fame playing career.

Only 57 of the cards are known to exist and few are in good condition considering they were printed between 1909 and 1911. At one time, hockey legend Wayne Gretzky owned one of the mint condition copies.

The record price for a trading card was by one of these T206 in 2016 for $3.12 million.

The "Casablanca" piano: $3.1 million

Humphrey Bogart, as Rick Blaine, tells Sam to "play it."

Sam strikes up a tune and begins playing "As Time Goes By" in 1942's "Casablanca," considered one of the greatest films of all time. The instrument is not only the center of a classic musical scene, but ends up being the focus of a major plot point.

Bonhams sold the piano in 2014 for $3.1 million.

The Maltese Falcon: $4.1 million

This, as Humphrey Bogart said, is "the stuff that dreams are made of."

The titular prop from the 1941 film actually has multiple copies, and the tale of the statue's authenticity is shrouded in as much mystery as the film it appears in. Even though light plasters from "The Maltese Falcon" have been authenticated, the most expensive one is 45 pounds of lead.

This specific falcon was sold in 2013 to hotel and casino billionaire Steve Wynn for $4.1 million.

The founding rules of basketball: $4.3 million

As auction house Sotheby's notes, basketball was invented, while most sports were created organically. This may be why a couple pieces of aged paper with the founding rules of basketball cost so much.

James Naismith reportedly created basketball in 1891 at the YMCA in Springfield, Massachusetts, where he worked. The rules of the game were typed with Naismith's own hand-written notes between the lines.

Sotheby's sold the document in 2010 for $4.3 million.

Babe Ruth's jersey: $4.4 million

Babe Ruth is still smashing records decades after his death. The jersey he wore for the New York Yankees in 1920 — his first year with the team — is the highest-selling piece of sports memorabilia to date.

The Bambino wore the gray wool jersey on the road and "NEW YORK" is stitched in blue letters across the chest. That year, Ruth hit 54 home runs, breaking the single-season record he set the year before with the Red Sox.

The dirt and sweat stained jersey was sold in 2012 for $4.4 million.

Audrey Hepburn's Ascot dress: $4.4 million

Audrey Hepburn's look from "Breakfast at Tiffany's" may be more memorable, but its this Victorian style dress from "My Fair Lady" that fetched millions.

Hepburn's turn as the singing Eliza Doolittle helped the 1964 film win the best picture Oscar As the dress' price attests, it also became a Hollywood legacy.

Owned previously by Debbie Reynolds, the dress sold in 2011 for $4.44 million.

James Bond's Aston Martin: $4.6 million

James Bond is one of the most recognizable movie characters of all time. Six actors have played the British spy in 24 movies, but no matter who the actor is, Bond still drinks martinis and drives Aston Martins.

Played by Sean Connery, Bond first drove the Aston Martin DB5 in 1964's "Goldfinger" and 1965's "Thunderball."

The very same car that 007 drove in these two films, gadgets included, sold in 2010 for $4.6 million.

The original Batmobile: $4.6 million

James Bond's car is not the only automobile to sell for $4.6 million

Adam West drove around Gotham in the Batmobile, which was originally a Ford 1955 Lincoln Futura. George Barris redesigned the vehicle into the Batmobile for the 1966 TV series "Batman."

Barris sold the car to a private buyer at an auction in 2013 for $4.6 million.

Marilyn Monroe's "The Seven Year Itch" dress: $4.6 million

One of the most iconic images in film history is of Monroe's white dress blown up by a puff of air from New York City's subway grating.

William Travilla, the costume designer for "The Seven Year Itch," kept the dress from the 1955 movie until 1971 when it was sold to actress Debbie Reynolds. Reynolds put the dress up for auction in 2011 along with other pieces of film memorabilia.

The dress fetched $4.6 million from an anonymous buyer.

Marilyn Monroe's "Happy Birthday" dress: $4.8 million

Monroe's dresses were a big deal.

The actress wore a nude dress with 2,500 rhinestones to President John F. Kennedy's 45th birthday party. The 1962 bash at New York's Madison Square Garden was one of Monroe's last public appearances before her death in August.

Monroe originally purchased the dress she sang in for $12,000. Ripley's Museum purchased the dress in 2016 for $4.81 million.