'Barbie' and 'Oppenheimer' are opening on the same day — here are 16 more times 2 huge movies were released simultaneously

15 years before "Barbie" and "Oppenheimer" faced off at the box office, WB and Universal squared off with "The Dark Knight" and "Mamma Mia!"Warner Bros., Universal Pictures, Warner Bros., Universal Pictures

• "Barbie" and "Oppenheimer" are both being released in theaters Friday.
• It's not the first time two huge movies both dropped on the same day.

Greta Gerwig's "Barbie" and Christopher Nolan's "Oppenheimer" are releasing on the same day in theaters in an event that's become known as "Barbenheimer" online, but it's not the first time two big-budget studio films have been released on the same day.

This isn't even Nolan's first time as part of a big summer-movie showdown.

There are only so many release dates per year and, sometimes, it's perfect for counter-programming.

Universal Pictures and Warner Bros. previously battled at the box office 15 years ago when Universal's "Mamma Mia!" went up against Nolan's critically beloved "The Dark Knight" in July 2008.

Heath Ledger's Joker performance helped WB's Batman sequel easily edge out the musical rom-com that opening weekend. However, both were huge successes: "The Dark Knight" made over $1 billion at the box office while "Mamma Mia!" brought in more than $600 million.

Insider rounded up some of the most unexpected movies released on the same day.