10 fast-food menu items you didn't know were more than 50 years old

• Many popular fast-food items were invented decades ago and remain unchanged.
• Chick-fil-A's chicken sandwich uses the chain's original recipe.
• Other fast-food chains have similar menu items from when they first opened.

Many chains are experimenting with new menu items, like Taco Bell's lineup of Cheez-It items , as well as expanding upon old favorites — think Burger King's Fiery Bacon Whopper or Wendy's new saucy nuggets.

While introducing new and exciting menu items is one way to grab a customer's attention, there's also something to be said for chains keeping their oldest, most popular menu items at the forefront of their businesses.

From McDonald's signature Big Mac to the original Chick-fil-A chicken sandwich , which uses the same recipe in restaurants today, these fast-food menu items have stood the test of time.

Here are 10 fast-food menu items that you probably didn't know were more than 50 years old.

McDonald's has sold hamburgers since it opened in 1940.

The first McDonald's restaurant , a small barbecue joint owned by Richard and Maurice McDonald, opened on May 15, 1940, in San Bernardino, California.

According to a photo of an early menu , the restaurant sold its "famous" barbecued beef, ham, or pork, as well as simple hamburgers.

In 1948, the McDonald brothers switched the concept , turning their barbecue restaurant into a burger restaurant and adding its now iconic items like hamburgers and cheeseburgers to the menu.

In 1955, Ray Kroc opened the first McDonald's franchise location. Kroc would go on to build McDonald's into the global chain we know now.

In 1965, McDonald's introduced the Filet-O-Fish sandwich nationwide.

Smithsonian Magazine reported that the Filet-o-Fish was created by Lou Groen, a McDonald's franchise owner in Cincinnati, in 1962 after he realized hamburger sales were declining on Fridays during Lent.

To increase sales at his restaurant, he decided to start selling a fish sandwich topped with tartar sauce.

The sandwich was such a hit that three years later, it was made available nationwide and has remained on McDonald's menus ever since.

McDonald's added the now-iconic Big Mac to its menu in 1967.

The Big Mac is arguably McDonald's most famous burger , but it wasn't added to menus until over a decade after franchises opened.

The burger's ingredients then remain largely the same as they do now: a double-stacked bun, two beef patties, shredded lettuce, pickles, and a Thousand-island-style sauce.

However, McDonald's recently tweaked its most iconic burger to have a softer bun, meltier cheese, and more sauce.

In 1957, Burger King released its signature burger, the Whopper.

According to Encylopedia.com , the Whopper originally cost just 37 cents , compared to Burger King's original burger, which cost 18 cents.

Although the Whopper now costs around $7 , prices vary by location. It still comes with sauce, cheese, lettuce, pickles, and tomato piled on top of a larger patty.

Chick-fil-A created its original chicken sandwich in 1964.

According to the chain , Chick-fil-A founder Samuel Truett Cathy tried hundreds of recipes for the original chicken sandwich before finalizing his famous recipe, which featured a fried chicken fillet with two pickles on a toasted butter bun.

Despite Chick-fil-A's significant growth over the years — the company generated $21.6 billion in sales last year — the chicken sandwich has largely stayed unchanged.

In-N-Out added "animal style" burgers to its menu in 1961.

In-N-Out started selling the first "animal-style" burgers after customers began requesting extra spread and grilled onions on their burgers. The "secret" recipe is still the same as it was in the 1960s.

The burgers are made with a mustard-cooked beef patty, lettuce, tomato, pickles, extra spread, and grilled onions.

In 1963, In-N-Out began serving its famous Double-Double burger.

The Double-Double , In-N-Out's version of a double cheeseburger, is now one of the most popular menu items.

It's also available in a variety of different styles, from "protein-style" sandwiched between two lettuce-leaf "buns" to animal-style.

White Castle began selling its sliders in the 1920s.

White Castle is often regarded as the first fast-food hamburger chain in America.

Founded in 1921 by Billy Ingram as a family-owned business, the fast-food establishment originally sold 5-cent, small, square hamburgers "by the sack," according to the chain . They would come to be known as "sliders."

In 1962, White Castle began selling cheeseburgers.

Taco Bell offered just five menu items when it opened in 1962, including tacos and burritos.

According to a vintage photo of the first Taco Bell menu, pictured above, each item cost just 19 cents, and the menu featured traditional Mexican favorites like frijoles, tostadas, burritos, and tacos.

Quite a few of Taco Bell's original menu items, including tacos and burritos, remain on the menu in some form, though the ingredients have likely changed from classic versions to more creative menu items like the Doritos Locos taco or grilled-cheese burrito .

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