Violence is a recurring theme at Donald Trump's political rallies. That fact has not been lost on city officials in Cleveland—host city to next month's Republican National Convention, where (presumably) Trump will become the Republican nominee for president. Thousands of officers from multiple agencies will coordinate to control the tens of thousands of visitors expected to inundate the city—and prevent those crowds from transforming into mobs. But police won't be the only ones keeping things in check. To keep things civil, Cleveland will leverage the fabric of the city itself.

Local and federal officials are cordoning off a 3.3-square-mile city-within-a city: the “Event Zone.” That's where security will be tightest, access controlled, and protests and other activity regulated. No tennis balls, baseballs, umbrellas with metal tips, ladders, sticks, poles, strollers, flashlights, balloons, or bike locks allowed.

Radiating outward from Quicken Loans Arena, the site of the convention, the Event Zone involves Cleveland police, the FBI, FEMA, and the US Secret Service. Closer to the arena, only people with the right credentials will be able to get into the “hard zone"—which officials won’t define until just before the convention. "It’s not only the folks inside that ring that need to be protected. We also have to focus outward and protect the people in the city as well," says Jason Porter, Central Region Managing Director for Pinkerton, a private security firm with clients at the convention and outside it.

City of Cleveland

This isn't a new idea, of course. From the walls that used to protect cities to Baron Haussmann's barricade-proof boulevards cutting through the labyrinthine arrondissements of Napoleonic Paris, planners and security forces have relied on the idea of defensible spaces to keep some people safe and others confined. Using the street grid to establish concentric rings that become increasingly secure as they progress inward is typical of large-scale events. Local police take the outer ring, and federal security agencies take charge of the rings nearer the bullseye.

But national political conventions have a democratic function and democratic obligations. So within the Event Zone—ironically almost the same size as Baghdad's famous, nominally secure Green Zone–a few spaces will serve as public gathering sites. Willard Park and Perk Plaza, northeast of Quicken, will be protest, congregation, and public art zones. And the city's Public Square, a 10-acre, 18th-century-style green less than half a mile from the convention and recently redesigned by the famed James Corner Field Operations, will serve as a “Speakers Platform,” for major speeches and performances. City officials have also established three “vending zones,” scattered within the perimeter, and a 1.5 mile parade route along Carnegie Ave., south of Quicken.

To the groups likely to protest the Republicans, that's not enough. "What the city has done here is draw a gigantic blanket area that covers most of downtown Cleveland," says Elizabeth Bonham, staff attorney for the American Civil Liberties Union of Ohio, which has filed a lawsuit hoping to reduce the Event Zone's size and restrictions. "When the government takes the extreme step of limiting speech and assembly in any way, the burden is on them to justify that those restrictions are reasonable," Bonham says. "Here there are no alternatives."

City officials, as you'd expect, disagree. In a press conference, Cleveland mayor Frank Jackson called the Event Zone and other crowd control measures "an attempt to balance between safety, security and constitutional rights of people and ensure we have a successful convention."

City of Cleveland

Finding the right balance would keep people at the convention safe but allow for free expression. Too many restrictions risk "security creep," a barely perceptible increase in security measures that eventually becomes untenable. "It’s incredibly undemocratic, but it’s the new normal," says Scott White, a cybersecurity expert at George Washington University. "I think issues of national security trump a lot of things now."

"Pardon the pun," he adds.