And those visitors keep coming: roughly a million people visit Dealey Plaza every year, about two-thirds of them from outside Texas. An appellate court ruled in March that the First Amendment gives vendors the right to set up shop in the plaza and sell materials related to the assassination.

The landscaped areas on both sides of that stretch of Elm, including the berm known as the "grassy knoll," are often manned by conspiracy theorists. One of them, Robert Groden, reportedly first added the white X to the street, indicating the spot over which Kennedy's limo was driving when he was hit.

The memorial by Philip Johnson, for its part, also symbolizes the city's deep ambivalence about commemorating the assassination. A spare cenotaph, or open tomb, designed to be built in marble, it was instead cast in cheaper concrete. And its location east of the assassination site suggested an effort to tuck the history of that day away.

"Everyone in town wanted to get away from Dealey Plaza," said Judith Segura, a historian who helped lead the fundraising effort to repair the site. "They didn't want the memorial to be right there. They thought that would be ghoulish."

Dallas architects Good Fulton & Farrell produced a master plan to restore the plaza in 2001. More recent work has been carried out and partly paid for by the city, bringing the total spent to roughly $2.5 million.

"We had to really shame the city into it," Segura said. "We went to the city and said, 'Look, we're going to be the focus of worldwide attention in 2013.'"

Officials ultimately decided to restore the pergolas and fountains to their original design and the landscape — the oak trees, bushes and the grassy knoll itself — to approximate the way it looked on the day of the assassination. The Sixth Floor Museum has produced a cellphone walking tour of the plaza that begins in front of the Book Depository and ends atop the triple underpass.

By the standards of Dealey Plaza's tortured history, that's progress of a sort.

For the 90-minute memorial program, which will include remarks by historian David McCullough, Dealey Plaza will be closed to traffic and perhaps temporarily resemble a traditional public plaza.

But after the stages and bleachers come down, Elm Street will be opened up again to cars. And Dealey Plaza will go back to being what it's been for 50 years: an unlovely, architecturally unresolved prick on the city's conscience.

If Kennedy had been shot inside a building, it's possible that Dallas would have demolished it by now — just as the city nearly saw the Book Depository come down. And just as the Los Angeles Unified School District demolished the Ambassador Hotel on Wilshire Boulevard, where Robert F. Kennedy was shot five years after his brother's death.

So maybe, for the sake of national memory and historic preservation, it's a stroke of macabre luck that the assassination happened in this ordinary and seemingly forgettable location.

You can't raze a spot in the air above a stretch of pavement way you can raze a building. You can ignore it or be vexed by it, both of which Dallas has done over the years. But a wrecking ball swinging through empty space doesn't accomplish much.

christopher.hawthorne@latimes.com