When you think of America’s top fast food chains, White Castle isn’t near the top of the list. Sure, White Castle is a household name and a massive chain, but it’s no McDonald’s or Burger King now is it?

But what if I told you that White Castle is the most important chain of them all? Or at least it was.

Walter Anderson and Billy Ingram founded White Castle in Kansas in 1921, becoming one of the first restaurants to operate under the modern fast food model. McDonald’s wouldn’t copy White Castle’s operating procedure for another 20 years. The very fast food system that we all love to hate today comes courtesy of the Castle and its sliders.

Back in the 1970s it felt like every street corner held a White Castle, each with the restaurant’s distinctive look. Here are 20 photos of what White Castle looked like in the 1970s.