A tall barrier separates two worlds. To the south, a crowded Mexican border town. To the north, beyond a heavily patrolled no-man's land, the lure of work and a better life in America.
The 2.5 meter (eight-foot) tall metal barrier has dramatically reduced the number of illegal immigrants crossing the border in the busy San Diego area, in the far southwestern United States.
Critics, however, say this has just forced the migrants to walk miles into the open desert to get around the wall, resulting in thousands of deaths.
Security along the 3,200 kilometer (2,000 mile) border with Mexico is a key factor in the debate over overhauling US immigration policy and figuring out what do with the 11 million people already living in the country illegally.
From a border hilltop near San Diego, the impact of the barrier is clear.
"Generations and generations of smugglers have lived in this area," said Border Patrol agent Timothy Hamill as he gestures south to a working-class neighborhood in Tijuana, Mexico.
From the hilltop one can see the waves of the Pacific Ocean to the west. To the east, the fence crawls over rugged hills into the horizon.
The crow of roosters can be heard from the Mexican side. In one poor Tijuana neighborhood, La Libertad, frugal residents use the barrier as a wall for their humble homes.
Armed US Border Patrol agents in pine-green uniforms patrol the open strip of desert between the wall and a secondary chain link fence on the US side.
Giant banks of stadium lights illuminate the border strip at night. Agents monitor the area around the clock using 59 cameras on 14 observation towers.
As recently as 20 years ago migrants would cross the border in large groups.
But, starting in the 1990s, agents began to raise a barrier of welded steel panels along the busiest parts of the border.
In the San Diego area, the steel fence runs some 90 meters (300 feet) into the Pacific Ocean, then east for 45 miles. A secondary chain link fence topped with razor wire runs for 13 miles.
Detentions dropped from around 400,000 a year before the wall to 28,000 last year in the San Diego area alone, Hamill said, while authorities have increased their haul of captured illegal drugs nearly 65 percent since 2005.
Along the route Hamill points to signs of tunnels under the border that have been dug, and sealed, over the years, as well as various holes in the wall.
"The border is more secure than it has been in the past," Hamill said. "But we definitely still have challenges to face. Protecting America is a very challenging mission and is very important to remain vigilant."
-- A deadly detour? --
Arrests may be down, but the undocumented migrants are still coming, says Enrique Morones, an activist with the group Border Angels.
The barrier and the increased security has meant a rising death toll among migrants who now make a wide detour into the desert to avoid detection.
Morones estimates there have been some 10,000 deaths along the whole border.
"Before they built the wall, one or two people would die every month. Since the wall was built, one or two people die every day," Morones told AFP. "The wall doesn't stop them, it just delays them."
The official Border Patrol figures are lower but still stark: 5,570 have died crossing into the United States illegally between 1998 and 2012.
Morones and his volunteers leave bottled water in parts of the desert where illegal migrants are known to cross.
The majority of the illegal border crossers are peaceful migrants in search of an honest job, according to Morones.
"Most of them are like the great-great-grandparents of those Border Patrol agents when they came. They're not criminals, they're just looking for opportunities," he said.
Unlike years past, when it was a free-for-all, migrants today usually pay smugglers known locally as "coyotes" a handsome sum to get around the agents and across the border.
One 38 year-old undocumented Mexican mechanic told AFP he often saw human remains on his frequent journeys across the desert into the United States.
"I know that wall very well," he boasts.
But, with the increased security, he said he has chosen to stay north of the border, and even bought false identification papers in case agents stop him as he travels north to Los Angeles to visit his young son.
Tomas, another one of the 11 million undocumented migrants living in the United States, scoffs at the idea that the wall would stop people like him.
"As long as there is demand for labor from Latinos in the United States, there will always be a way to get around that wall," the 35-year-old Mexican told AFP.