DILLEY, Texas — On the side of a dusty highway about 70 miles southwest of San Antonio, more than 500 protesters gathered Saturday afternoon in front of the largest immigration detention center in the United States and chanted "shut it down" as facility guards watched from the other side of a barbed wire fence.

"We didn't come here to be criminals. We came here to work hard and put food on the table," said Marta, a 16-year-old immigrant who declined to give her last name, and whose aunt and young cousin are locked up as they wait for an immigration court to grant them asylum or send them back to El Salvador.

The detention center in Dilley, a South Texas town of about 3,600 people, was built in December 2014 to host up to 2,400 undocumented women and children who are seeking asylum. Protesters from all over the country — as far as California and New York — trekked to Dilley on Saturday to call for an end to family detention.

"Many of them are escaping from violence and torture, from abuse at the hands of gangs," said Sofia Casini, a detention visitation coordinator at Grassroots Leadership, an organization that helped orchestrate the protest. "To be put inside of centers with armed guards, where the kids are yelled at, it's all a re-traumatization process."

The Texas Tribune thanks its sponsors. Become one.

Immigration and Customs Enforcement (ICE) spokeswoman Nina Pruneda said in a statement Saturday that facilities like the one in Dilley are "an effective and humane alternative for maintaining family units."

"ICE insures that the Dilley center operates in an open environment and includes playrooms, social workers, educational services and access to legal counsel," she said.   

The South Texas Family Residential Center in Dilley — a euphemism, the protesters say, for a low-security prison — is one of two family detainment facilities in Texas, and the largest in the U.S.

"There's one issue with calling them residential facilities: They're locked up. They can't leave," said Bethany Carson, immigration policy researcher and organizer for Grassroots Leadership. 

In 2009, the U.S. Department of Homeland Security decided to stop detaining immigrant families at the T. Don Hutto Family Detention Facility in Taylor, after a lawsuit exposed poor treatment of detainees at the center — children wearing orange prison uniforms and receiving 12 hours of cell time each day and only one hour of schooling.

"After that, we thought that family detention had been eradicated," Carson said.

The Texas Tribune thanks its sponsors. Become one.

But a surge of immigrants from Central America in mid-2014 prompted the Obama administration to return to the practice of detaining families in secure facilities to deal with the influx.

At the opening of the Dilley center last year, U.S. Homeland Security Secretary Jeh Johnson warned immigrants coming into the country illegally that "it will now be more likely that you will be detained and sent back."

The same for-profit prison company that operated Hutto, Corrections Corporation of America, also runs the Dilley center.