BROWNSVILLE, Tex. — Salvador Castillo was yearning for tranquility when he became enchanted by a one-acre homestead close — but not too close — to the city, a place where cows graze beneath whispering mesquite trees on the property’s edge.

This was Texas living, the Afghanistan war veteran thought, not the thin-walled apartment and constant din that aggravated the emotional scars of his work providing security for Air Force operations. Castillo and his wife bought the home using military benefits and grew their family into their new neighborhood — about half a mile from a bend in the Rio Grande, near where it ends its journey through mountains and deserts and the valley, spilling into a sandy delta at the sea.

They never imagined a border wall could dissect their property someday. But the first letter, stamped with an official government seal, arrived about a year ago. Their neighbors, the Carrascos and Trevinos, got them, too.

The United States wanted permission to enter and survey their land — three homes targeted in two neighboring U-shaped Texas subdivisions — in preparation for construction of the Trump administration’s new border wall system.

“We were astonished,” Castillo said, noting that the government letter basically sought unlimited access to his family land with no preclusions. His wife, Yvette Arroyo, threw the first letter away, but the lawsuit that came next was a bit more intimidating. “We were like, ‘Hell no!’ We don’t like this. It’s very intrusive.”

President Trump aims to build 166 miles of border barrier in Texas, almost all of it slated to go on private land that the government has yet to acquire — thousands of parcels along the river, an unknown number of them occupied by their owners, including churches and single-family homes. No new border wall has been built on private land in Texas since the president took office, but land acquisition in the Rio Grande Valley is about to enter a new phase this week, as U.S. attorneys began filing initial petitions in court while making cash offers to property owners, according to Justice Department officials with knowledge of the process.

On Friday, the federal government filed its first land acquisition case to condemn nearly 13 acres of private property in the Rio Grande Valley, a parcel near the river levee in Hidalgo County. The owner was offered $93,449 in compensation for the land.

As the government pushes to accelerate construction of what Trump has promised will be a total of 500 miles of new barrier by the end of 2020, it is families like the Castillos, Trevinos and Carrascos that are in the way. Building a wall means more than cutting through desolate desert, grassy ranchlands, shrubby wildlife preserves or old vacant lots — it also means seizing land from working families.

The fight that probably will ensue pits Texans against Trump, who has long said he wants to take whatever land he needs to build his signature promise to America. Landowners, including some who support Trump, are preparing a legal fight that could stall the wall-building effort and lead to years-long court battles over private land rights, family homes and what the Trump administration deems a critical national security issue.

So far, the Trump administration has built about 85 miles of fencing, nearly all of it replacing older structures built before the president took office in 2017. The government broke ground on new border wall in the Rio Grande Valley on Nov. 1, but it was on land the government already controls.

The president has placed his son-in-law, Jared Kushner, in charge of the wall project, including the acquisition of private land. Kushner has urged the Army Corps of Engineers and the Justice Department to expedite the process and more recently has directed staff to begin building a centralized database of all the privately owned parcels along the border, according to two senior administration officials familiar with the effort.

Building additional wall on the southern border will require eminent domain. In the past, President Trump has taken an expansive view of eminent domain powers. (JM Rieger/The Washington Post)

The letters landowners have been receiving are the first step in what can be a contentious process, with the government seeking “right of entry” to conduct surveys on the properties and unfettered access for 12 to 18 months. Most landowners consent at first contact and eventually sell, according to attorneys familiar with the eminent domain process.

A growing number of South Texans have not signed those letters and are facing federal lawsuits seeking access to their land. Some said in interviews they have refused to sign because they have concerns about the process or oppose the border wall project.

The Brownsville neighbors, who are no fans of the wall, ignored the letters. One family threw it away. Then came the calls, the text messages and the visits from U.S. attorneys to their jobs and homes.

“I stopped answering the door,” Arroyo, a teacher, said of the multiple visits from lawyers, U.S. Border Patrol agents and Army personnel. “Going to battle against the federal government is not something we will win. But we are not going to take this lying down.”

Assistant Attorney General Jeffrey Bossert Clark of the Justice Department’s Environmental and Natural Resources Division said Congress authorized the Department of Homeland Security to acquire land, including by condemnation, “for the public purpose of protecting our nation’s international borders from such threats as terrorism, human trafficking, drug trafficking and illegal immigration.”

“When such takings become necessary, the government provides just compensation that is fair to both landowners and taxpayers,” he said. “When landowners disagree with the government over valuation, there is a transparent, court-supervised process for determining just compensation. The vast majority of these matters are resolved without litigation.”

U.S. authorities have filed more than twice as many land-taking lawsuits in 2019 as they did in 2018, indicating that more people are objecting to the government’s use of their land. The Texas Civil Rights Project, which is representing six border property owners pro bono, said the lawsuits signal that landowners are resisting. The nonprofit organization worked closely with activists to teach landowners that they are not obligated to sign their rights away, but many of the property owners cannot afford legal representation.

“These cases are just the tip of the iceberg,” said Ricky Garza, an attorney with the civil rights organization. “We don’t know how many others are prepared to fight back.”

If a court grants the government access, surveyors enter the properties to test the soil, run hydrology studies and determine how much land they need to take for the project. Federal officials sometimes don’t return, deciding a barrier cannot be built and instead work toward installing technology such as fiber optic cables, cameras or listening devices as part of what officials call the “border wall system.”

Rocio Trevino, who owns a home in the subdivision adjacent to the Castillos and Carrascos, denied the government access to survey until they could answer basic questions about what would happen next. The Trevinos signed over rights to a vacant lot they own that also lies in the wall’s path. But the idea of giving the government access to their family home was different.

Trevino voted for Trump and agrees that the nation needs to secure the border — the family has hurricane shutters over every window and door for security — but she is exasperated by the uncertainty and unresponsiveness of the process involving her property.

“What bothered me most is every time I asked a question, the government responded with, ‘We don’t know. We don’t know,’ ” she said.

With five children and a pet horse, the family was not comfortable with strangers entering the property at any hour. The only information they have seen is a map of their tract with a red box superimposed on the slice of the backyard the Trevinos presume could be taken from them. It is adjacent to the holding pen where they keep their quarter horse, Chief, and feet from a fenced-in swimming pool.

People who support the idea of a wall “might feel like it’s good and it’ll stop illegals, but when the wall gets into your space, well, nobody wants that,” said Trevino, 39, who owns a business consulting firm. “I am well aware that things are happening around us, but this is our space and we should have a say-so in whether we want it or not.”

The ordeal has shaken Trevino’s faith in the president, and she would not say if she would vote for him again next year.

Once past the surveying stage, the government will decide how much private land to take and what to pay for it; the government is obligated to offer fair market value as it takes title to the land. Even as negotiations begin, the federal government could own the land in as little as 90 days, attorneys said.

The problem for these three middle-class American families is that despite being relatively far from the waters of the Rio Grande, their property lines are within 50 feet of an earthen levee that marks the edge of the ever-changing waterway’s flood plain.

Wall construction elsewhere in the region involved cutting into the levee to build the concrete base that anchors tall steel bollards. The design includes “enforcement zones” or roads that hug the wall and are wide enough for agents to patrol in vehicles.

Elvia Carrasco has no idea if the metal markers seven feet inside her backyard fence line means that is all contractors will need, or if the construction will run right through the middle of her home.

After years of working and living in Minnesota, Carrasco and her husband moved south, living in a recreational vehicle in Brownsville for a few years before buying a home in 2015 large enough to fit her entire family for holiday reunions.

“Imagine fitting six adults and grandchildren into an RV for Christmas,” said Carrasco, 62, laughing as she tended to the young guava, plum and lemon trees in the backyard botanical garden she has cultivated. The survey marks cut into her garden.

The couple poured their savings and the money they earned from the sale of their other home into the down payment on their border home, and then spent tens of thousands of dollars on outdoor electricity and an aluminum shed Carrasco’s husband built as a “man cave.” Their border home is an oasis.

“Nothing happens out here,” Carrasco said. “Sometimes I spend all day outside pruning and talking to God and my flowers and plants about all this. I’m not going to let them take what we worked so hard to earn.”

With a partial wall near their homes, three neighbors in Penitas, Tex., react to President Trump’s call to expand the barrier on the Mexican border. (Drea Cornejo, Jon Gerberg/The Washington Post)

Castillo and Arroyo expect their property value will drop when the barrier is built, and they have suspended all home improvement projects, trying to ignore the cracked blacktop driveway and the failing brick exterior and waiting to repair the master bathroom.

Skinny PVC pipes poke out from the ground where the couple started and stopped installing a sprinkler system. The frame of an unfinished treehouse sits hollow in the middle of the backyard. Instead, the family is saving money in case they have to move.

“We’re kind of trapped,” Castillo said, his youngest son giggling in a tree swing and his daughters feeding grass to a passing horse they dubbed Philippe after the horse in the Disney film “Beauty and the Beast.” “Why am I going to invest in my property if I’m going to have to stare out at a wall or lose it entirely? I’m leaving. I can’t stay here.”

Castillo’s ancestors settled in the Rio Grande Valley in the late 18th century as ranch hands and saddlemakers. They are naturally “border people,” and more Texan than American, he said. When he moved into the home, he brought his great-grandfather’s gravestone along and placed it in the southeast corner of his yard — inches from a spray-painted wooden stake the government placed there in September. It is labeled RGV-HRL-7528-2.

He sees the effort to take his land as a betrayal of his service to the country, but he says he is trying to be realistic.

“This is what a certain majority of Americans wanted,” he said. “So because of their desire, I have to swallow it, accept it and take the hit. I guess this is service of a different kind to that America. It’s easy for them to judge; it’s not their backyard.”

Nick Miroff and Josh Dawsey in Washington contributed to this report.