Then it got really crusty.
Cops in the Windy City reignited the age-old debate on Wednesday, tweeting, "Saturday is #NationalPizzaDay. How will you celebrate, Chicago? Deep dish, or ol’ fashioned thin crust? Either choice beats New York-style slices. Like/RT if you agree."
The Twitter battle heated up leading up to Saturday, which is National Pizza Day.
The New York Police Department wasted no time in setting them straight, tweeting: "We recognize the slice of pizza on the right, but what’s the one on the left? Is there pasta in it?"
"That was almost as cheesy as a South Side deep dish. ALMOST," Chicago police said.
The back and forth did get cheesier. Literally.
Eventually, even Game of Thrones author George R. R. Martin jumped in to respond to the NYPD and ask: "Shall I send a dragon?"
Chicago Police responded, politely, but with a burn, "No thank you, good sir. In case you haven't heard, Winter is already here."
But New York just responded with a gif of King Joffrey choking.
Both sides took a bite of the opposing team's pies because every great battle requires sacrifice.
On Saturday, four Chicago cops sampled some New York slices -- outside the U.S. Pizza Museum, no less.
“It’s all right, but it’s not Chicago,” he said. "Sorry."
But the NYPD, being New Yorkers, couldn't let that be the last word.
On Friday afternoon, a group of cops tasted a Chicago pie outside of Manhattan's Lincoln Center.
"A little soft. Like your baseball team," one New York cop taunted.