MATAMOROS, Mexico — Shortly before dawn one Sunday last August, a driver in an S.U.V. picked up Christopher Cruz at a stash house in this border city near the Gulf of Mexico. The 22-year-old from El Salvador was glad to leave, but he was anxious about what lay ahead.

The driver deposited Mr. Cruz at an illegal crossing point on the edge of the Rio Grande. A smuggler took a photograph to confirm his identity and sent it using WhatsApp to a driver on the other side of the frontier.

The 3,000-kilometer trip had already cost Mr. Cruz’s family more than $6,000 and brought him within sight of Brownsville, Texas. The remaining 800 kilometers to Houston would cost another $6,500.

It was an almost inconceivable amount of money for someone who earned just a few dollars a day picking coffee beans back home. But he wasn’t weighing the benefits of a higher-paying job. He was fleeing violence and what he said was near-certain death at the hands of local gangs.

«There’s no other option,» Mr. Cruz said. «The first thought I had was, ‘I just need to get out of here at whatever cost.’ »

The stretch of southwest border has become the epicenter of the raging battle over the Trump administration’s immigration crackdown. One clear consequence of the tightening American border is that more and more desperate families are turning to increasingly sophisticated smuggling operations to get relatives into the United States.

Even with his family’s payment, he slept amid filth and vermin. Sometimes the smugglers identified him by a numeric code, other times by an assumed name. But as often as not, they simply called him «the package.»

For Mr. Cruz, it was worth it. «They can build as many walls as they want,» he said, referring to American officials. «They can send as many soldiers to the border as they want, but a people’s need and desire for a better life is stronger.»

A decade ago, Mexicans and Central Americans paid between $1,000 and $3,000 for clandestine passage into the United States. Now they hand over up to $9,200, the Department of Homeland Security reported last year.

That day at the Rio Grande last summer, the smugglers had gathered the migrants at the water’s edge. Mr. Cruz pulled off his khakis and T-shirt and paddled to the other side.

Once across, the small crowd of migrants began to sprint toward the five-meter steel security fence blocking their passage into the United States. Mr. Cruz had climbed halfway up the fence when he heard a helicopter overhead and saw patrol cars converging. Agents grabbed those already over the fence and began to arrest them.

«When I saw that, I slid down and I ran back,» Mr. Cruz recalled. He dived again into the Rio Grande, his only hope to escape back to Mexico.

Mr. Cruz grew up in San Miguel. Gang violence is endemic in the country, and Mr. Cruz dropped out of high school when the infamous MS-13 became too dangerous there. His family relocated to Berlín, which had less of a gang problem.

Mr. Cruz’s mother lived in the United States, but he was much closer to her brother there, an uncle he considered a father figure and called «Papi.» Mr. Cruz lived with his grandmother and younger sister. He also had a 2-year-old son.

The police had all but declared open season on gang-age men, Mr. Cruz said, and he and his friends were harassed and beaten by the security forces. Meanwhile, gang members regularly threatened him.

«That is the reality of El Salvador,» he said. «You are scared of both, the gangs and the police.»

Mr. Cruz’s uncle used WhatsApp to contact a woman in Mexico representing a smuggling network, who became the point of contact throughout Mr. Cruz’s journey.

The uncle, who now has legal status in the United States after arriving illegally years ago, spoke on the condition of anonymity because he feared he could be prosecuted for trafficking a family member.

Mr. Cruz’s aunt and uncle earned enough to advance him the money for the journey, but Mr. Cruz would have to pay them back. They wired $800 to El Salvador. «Any opportunity you have to connect, send me a message with your location,» the uncle wrote.

«Activate Find My iPhone so you can find out my location from the iCloud,» Mr. Cruz answered. «That way you’ll know the route I’m taking.»

In the beginning, it was almost like being a tourist. Mr. Cruz legally crossed into Guatemala in a pickup truck driven by a smuggler at La Hachadura with his national identity card.

The driver took him by bus to the capital, Guatemala City. They transferred buses and traveled to Huehuetenango, which serves as a jumping-off point for the Mexican border.

They spent a night in a cheap hotel and traveled the next day to La Mesilla along the Mexican frontier.

To skirt the border police outpost, the smuggler directed Mr. Cruz to a nearby industrial area where he walked alone up a gravel path and into Mexico. For the first time, he became an illegal immigrant.

Mr. Cruz boarded a minibus to begin his trip through the southern state of Chiapas. As instructed by the driver, at toll plazas he hunched down and covered himself with the passengers’ backpacks, suitcases and packages.

Just two days into Mr. Cruz’s journey, his family had to wire the smugglers $1,900 to get him through southern Mexico.

After several nights in Chiapas, Mr. Cruz climbed into the cab of a tractor-trailer and rode alongside the driver. Officers stopped the truck for a routine check, and after seeing Mr. Cruz’s Salvadoran ID, realized that he was in Mexico illegally. They demanded money or else they would deport him, Mr. Cruz said. He fished out $170 he had hidden in his shoes.

On subsequent traffic stops, the bribe for the police was always the same: 1,500 Mexican pesos, or about $84. The fourth time he was stopped for a payoff, the cop simply said, «You already know how much this is.»

Mr. Cruz made it as far as Puebla, southeast of Mexico City. His family wired $450 to the smugglers.

After a week there, Mr. Cruz hid in the sleeping compartment of a tractor-trailer for the overnight drive to Monterrey.

Far from Monterrey’s downtown, behind a front gate, the windows and doors were shut and barred on the house where Mr. Cruz was kept. Trash was everywhere. Ants and cockroaches crawled indoors.

«It was like a prison,» Mr. Cruz said.

At night, Mr. Cruz said, he couldn’t sleep, with mice and insects running over him.

He was stuck there for four days. His uncle sent $2,800, and they carried him onward to the border state of Tamaulipas, just below southern Texas.

Mr. Cruz was sick. He was eager to leave, but his coughing spasms gave the smugglers pause. They didn’t want him giving their position away.

His family sent $180 to the smugglers, who said half would go toward medicine and half for a backup phone. Doses of cough syrup, along with several days of rest, seemed to help. That Saturday night Mr. Cruz wrote to his uncle, «At 4 o’clock in the morning I go.»

The region, where the Rio Grande coils and bends in switchbacks, has become the central battleground for illegal entries. Some 138,000 people were caught trying to cross here in 2017.Blimps equipped with cameras provide the Border Patrol with video surveillance. Migrants trip seismic sensors with their first steps on American soil. The number of Border Patrol agents has grown to about 20,000 from roughly 9,000 in 2001.

The smugglers gathered Mr. Cruz and more than 20 other migrants and crammed them into the back of an S.U.V. Wedged into a corner of the trunk with the weight of migrants crushing down on him, Mr. Cruz struggled to catch his breath.

Once at the Rio Grande, he swam to the other side, while those who couldn’t swim were pulled on inner tubes. The migrants in his group began to mount the border fence. But the Border Patrol descended. He realized he had to turn back, across the river.

As was customary, the smugglers would give him three tries to make it across safely.

His second attempt, at another crossing nearby, was even shorter than his first. Border Patrol agents swarmed the group as they made landfall. Mr. Cruz again swam back.

The sun was low by the time the smugglers brought the migrants to their third crossing point. They said the spot, more isolated, was usually reserved for moving drug shipments, more valuable than migrants.

Of the 17 people left, Mr. Cruz recalled, five were women, including one who was pregnant and another in her 50s. He wondered how they would make it, but his family had warned him: Worry about yourself. Do not stop for anyone.

Mr. Cruz could hardly believe the determination of the pregnant woman as they emerged from the river. But the older woman slipped behind and fell to the ground. The guide did nothing. «He just left her there,» Mr. Cruz said.

It was only a short drive to a parking lot where the smugglers separated the group into different cars, depending on their destinations. Mr. Cruz and five others got into a Cadillac headed northwest to a stash house in McAllen, Texas.

After a day and a half, Mr. Cruz huddled with four other migrants in the sleeping compartment of a tractor-trailer headed to San Antonio.

Mr. Cruz was brought to one last stash house and was stripped to just his boxer shorts, essentially a hostage until the final payments were made. Two days passed.

His family had to transfer the remaining $6,500 to the smuggling network. Although a record $28.8 billion in remittances was sent to Mexico last year, the authorities regularly flag suspicious transactions. Mr. Cruz’s uncle had to break up the sum into smaller, less conspicuous transfers.

Only when the final installment arrived in Mexico could Mr. Cruz go. «They gave me my clothes to put back on, and they blindfolded me again,» he said.

The smugglers drove him to a gas station. There he saw the familiar face of his uncle. Mr. Cruz began to cry.

Relief at finishing his journey did not last long. Mr. Cruz was now in an unfamiliar country, where he did not speak the language and could not legally hold a job. He would have to hide in plain sight. He was $12,630 in debt. But, he said, at least he didn’t fear for his life. «Here I know I’m safe,» he said.

Mr. Cruz looked ahead to earning enough money to begin the cycle again, paying for his son, his sister and his grandmother to join him. «I dream of bringing them over here,» he said.

© 2018 The New York Times