It was the 1930s in South Philly, and Pat Olivieri ran a hot dog cart near the Italian Market.

One afternoon, Olivieri couldn’t stomach the thought of another hot dog for lunch, so he sent his brother to the butcher.

They chopped up and seasoned the fresh beef, topped it with onions and laid it across a bun. In that moment, a cab driver, also craving a change, opted for the brand-new concoction and convinced Olivieri he was on to something.

And so, just like that, Pat’s King of Steaks was born.

Jim’s Steaks followed suit in 1939, then Geno’s Steaks opened up shop in the 1960s.

According to The Philadelphia Inquirer, Olivieri never intended to put cheese on the sandwich so that his Jewish friends could still come by and enjoy one.

Cheese would be added years later in the 1950s according to Mashable, and the sandwich is now either served with Cheez Whiz, American cheese or Provolone cheese.

There’s just one rule: don’t use Swiss.

Make a pledge and become a member of Italian Sons and Daughters of America today.