As the drone of the morning traffic subsided, Martin, a 30-year-old Miami native with high cheekbones and a thin chin-strap goatee, rose from the two old chairs he'd pushed together to make a bed, brushed his teeth, and picked up a can of black spray paint. He used it to write just one word, which is still emblazoned—in giant letters—on the concrete embankment below the Julia Tuttle: why?

Ten months later, Martin is still under the bridge, and the number of men living with him has doubled. They have different backgrounds but one thing in common: They are all convicted sex offenders. Fourteen men, ranging in age from 30 to 83, call this place home. Some sleep in cars among the pilings, others in grimy Wal-Mart tents wedged beneath the bridge. Martin, who spent two years in jail after being convicted of exposing himself to a 16-year-old girl when he was 19 or 20 (a crime he says he didn't commit), no longer has to wear the black GPS monitoring device that many of his neighbors do. He finished his five-year probation in 2006, but he can't find a place to live that complies with the county's residency laws. So Martin is forced to live here—in a colony under an overpass where the amenities include a generator, a composting toilet, and a workout area with a bench and free weights—indefinitely, because he and the other men were ordered here by law-enforcement authorities.

"Take a picture if you want," says Martin, showing off his driver's license. The address next to his photo reads UNDER THE JULIA TUTTLE CAUSEWAY.

In the past, very few states required convicted sex offenders to register their home addresses. That changed in 1994, when, following the abduction of an 11-year-old Minnesota boy, Congress passed the Jacob Wetterling Crimes Against Children and Sexually Violent Offender Registration Act. The legislation gave states the option of establishing a registry or losing 10 percent of their criminal-justice funding (all chose the former). Florida, like many states, barred offenders from living within 1,000 feet of schools, parks, playgrounds, public-school-bus stops, or other places where children congregate. Then in 2005, when a 9-year-old girl named Jessica Lunsford was murdered by a 47-year-old drifter in Homosassa, Florida, communities across the state and country converted their outrage into more legislation. Miami Beach expanded its restricted areas to 2,500 feet—effectively banishing every offender in town. The situation escalated: County commissioners, nervously watching as the displaced spilled eastward into their districts, extended Miami Beach's local limits to the whole county. Other counties followed suit. There are now 128 local ordinances in Florida that limit where a sex offender can live. Critics say these laws are only making it harder for authorities to keep track of offenders. Some are just disappearing—meaning that they can show up in other towns, where no one knows their history, and face no monitoring from authorities. Since 2005, the number of absconders has tripled in Florida—in Miami-Dade, the increase is tenfold. Nationwide, according to the National Center for Missing & Exploited Children, at least 100,000 sex offenders have become noncompliant. No one knows where they are.

"Burn that shit!"

Patrick Wiese, a skinny, sunbaked 47-year-old with a thick moustache and no teeth, is drinking a Miller High Life outside his tent on an early-May afternoon. The old man he's talking to, Hector Fernandez, sits shirtless on a battered stool, fanning himself with a piece of cardboard. Fernandez, a sixtysomething who likes to wear socks with his sandals, has taken on the role of maintenance man. Wiese gestures at the trash heap on the beach.

"Burn that shit!" he says again.

In the colony at the Julia Tuttle, Wiese is something of a den mother. He works—at a sub shop a few miles west—and when the generator "took a shit" a while back, he says, he shelled out $118 to fix it so the guys on parole could keep their monitoring devices charged.

"The only reason I do all this—it ain't for me," he says, crouched on a piling. "I had a friend tell me, 'You know what? You're there for a reason.' I thought about that for a few days. And then the generator broke down, and lo and behold, I was there for a reason." Almost three years ago, Wiese was arrested for child molestation after, he says, "letting" his 9-year-old stepdaughter touch him through his shorts. He spent 18 months in jail and has eight years of probation left to serve. (Wiese is currently back in jail, pending a court date, for not reporting to his parole officer.)

The shack where a man nicknamed El Viejo—at 83, he's the oldest resident of the camp—lives is at the base of the bridge's embankment. Eight months ago, having been sentenced to 10 months' probation after being convicted of child molestation, he couldn't make it up the hill, so Wiese and Martin hammered together a cube for him down there and covered it in Coors Light banners to keep the wind out.

Wiese and Fernandez bullshit about bridge life for a couple of hours until around sundown, when fellow bridge-dwellers begin returning from work in their cars. Parolees have a 10 p.m.-to-6 a.m. curfew. Wiese gives up on his maintenance man and squirts gasoline on the trash heap. The guys gather around, cracking open beers and watching the trash burn. Around midnight, Roberto (not his real name), a 53-year-old architect and interior designer with white hair and wire-rim glasses, wanders off alone with his Solo cup of Heineken.

"I used to live somewhere there," he says, looking out at the Miami skyline. "That's the sad thing." Seven years ago, Roberto went to jail for having sex with his 13-year-old daughter—a crime he describes only as "horrible." He wears two oversize T-shirts to conceal his GPS box and sleeps in the cab of his white pickup truck every night.

Just then El Viejo emerges, dressed in crisp Dickies and shuffling slowly past the fire.

"I live in that house!" he says, pointing at the shack. "Beautiful view! You can go fishing!" The guys smile at him. There's not much else they can do. El Viejo is deaf. Last year he was arrested for fondling three children after luring them with a puppy. It wasn't his first offense.

Parole officers visit the Julia Tuttle five times a week to check up on the offenders, says Gretl Plessinger, spokesperson for the state DOC. The three-year anniversary of the colony is approaching, and they're worried that some of the men who are frustrated by the conditions will disappear. "We don't like them being homeless," Plessinger says. "It's not good for them—it's not good for society—and our concern is that they may abscond."

The community under the Julia Tuttle isn't the only cluster of sex offenders in the country. Roughly 80 offenders live in the 30th Street Men's Shelter in Manhattan, according to the state registry. Nearly 100 live in a trailer park outside St. Petersburg, Florida, and there are around 45 in a small town on Long Island, in New York. But nowhere has a group of homeless offenders become so established as under the Julia Tuttle Causeway. And it's likely that the men are going to be there for a while, because no local politician wants to be seen as soft on sex criminals.

"It's a ticking time bomb," says Florida state senator Dave Aronberg, who represents the Fort Myers area. "You have homeless sex offenders roaming the streets. And once you're off probation, no more curfew. You can spend all day and all night sitting in a park and looking at kids. This is a scandal that the politicians created. Now the public is in danger because these well-intentioned laws have backfired."

Kevin Morales, who sleeps in his truck alongside the causeway, spent 10 months in jail and was given 10 years' probation for an offense that happened more than a decade ago. Before the law changed, Morales, who owns a glass business, had been sleeping above his shop in an industrial part of town that fell outside the state's 1,000-foot restrictions. But when Miami increased the distance to 2,500 feet, he says, his probation officer gave him five days to find a new residence or face arrest. Morales went through dozens of options, all of which fell through. With time running out he signed a lease and put down a $2,400 deposit for the first two months' rent on a place that complied with all the ordinances.

"That was Friday," he says. "On Monday I get a call from my probation officer telling me I can't live there because the building has a pool, and that's a place where kids congregate." Morales lost his deposit, and because he couldn't secure a permanent address in time, he says, his probation officer gave him a choice: Go to jail or sleep under the bridge.

"You're telling me I have to go live under a bridge?" he said to his officer.

"Look, you can ignore it," Morales remembers him saying, "and if you want to go to jail, that's fine."

He chose to live under the Julia Tuttle, which is far enough away from residential districts that it is largely overlooked. One day last August, however, Morales says, a bridge dweller named Marcos was going to work, rounding the concrete embankment on his way to the highway above. As he lifted his foot over the guardrail, someone lobbed a bottle at him from a car. It shattered on impact and lodged itself in Marcos shoulder.

"If you left it up to the public," Morales says, "they'd burn us at the stake."

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