TAMPA, Fla. -- As soon as Donald Trump mentioned the southern border during a Friday-night rally in a packed sports arena, someone in the audience shouted: "Build that wall!"

Trump stopped talking, smirked, leaned into the microphone and joined: "Build that wall! Build that wall! Build that wall!"

Soon the crowd of 11,000 was chanting in unison, with Trump jerking his right hand up and down like a band director. Even when he stopped, they kept going.

What started as a policy position months ago -- building a massive wall along the 2,000-mile-long border with Mexico to keep out illegal immigrants, terrorists and drugs -- has morphed into a cultural icon, rallying cry and, at times, punchline.

"The wall -- the wall -- everyone loves it, everyone," Trump said Friday night. "I love the wall."

Trump has been criticized for not providing details on many of his policy proposals, like replacing the Affordable Care Act, taking out the Islamic State terrorist organization and saving Social Security. But he has endlessly elaborated on his plans for the wall, saying it will be "artistically beautiful," taller than any ladder and one foot taller than the Great Wall of China. He likes pointing to the ceiling of arenas as a frame of reference. Experts have said that such a wall would cost billions to construct, but Trump has said that he will force Mexico to pay for the construction. When former Mexican president Felipe Calderon said Saturday that his country wouldn't pay a cent for Trump's "stupid wall," the candidate added another 10 extra feet to the theoretical wall's height.

The wall nearly always comes up in Trump's rally speeches and it often prompts laughter and applause -- and protesters with signs outside the rallies. The wall is so popular with his supporters that Trump gleefully realized at a recent rally that he could drown out a protester who was starting to act out by suddenly switching topics and mentioning the wall. At Trump's rally at the University of South Florida in Tampa on Friday, one guy dressed up as the wall, wearing a white bodysuit with bricks drawn on it and a sign reading: "The Trump Wall."

As the promise of the Trump's wall becomes bigger, grander and more fantastical, it is sometimes difficult to tell if Trump is joking or sharing a serious policy development. Trump said Friday that he's dead serious.

"These people come up to me, they say: 'Donald! You don't really mean we're going to build a wall, do you?' And I say, I say: 'Absolutely, we're going to build a wall,'" Trump said, as the crowd yet again cheered. "Hundred percent."

Trump said that some Europeans want to build walls around their countries, given the burst of refugees fleeing violence in Syria and other Middle Eastern countries. Constructing such a wall is not as dramatic as it sounds, Trump said, given that China built the 13,000-mile-long Great Wall more than 2,000 years ago.

"They didn't have Caterpillar tractor, by the way," Trump said. "Thirteen-thousand miles long. It's a massive wall, it does work. You know, the walls work. Ask Israel -- walls work. Believe me."

He then smiled and said: "Okay, are you ready? Who's going to pay for the wall?"

The crowd responded: "Mexico!"

"Who?" Trump said.

"Mexico!" the crowd said, even louder the second time.

"We -- not me, we -- are so tired of being pushed around by these other countries, like we're a bunch of dummies," Trump said. "Not gonna happen anymore. Okay? Not gonna happen. Not gonna happen."