A man watches across the border from Tijuana, Mexico, on October 12, 2017 a prototype of US President Donald Trump's US-Mexico border wall being built near San Diego, in the US, Following up on President Donald Trump's campaign promise to build a wall along the entire 3,200 kilometre (2,000 mile) Mexican frontier, the Department of Homeland Security began building prototypes for the barrier along the border in San Diego and Imperial counties, as it announced in August. Guillermo Arias | AFP | Getty Images

Nine months after President Donald Trump took office, the first tangible signs of progress on one of the central promises of his campaign have appeared along the U.S. border with Mexico. A couple of miles from the bustling Otay Mesa border crossing in San Diego, eight towering chunks of concrete and steel stand as high as 30 feet tall against the sky, offering possible models for what Trump has promised will one day be a solid wall extending the full length of the southern border, from California to Texas. Whether any of the eight different prototypes, constructed over the last month, become part of an actual wall remains highly uncertain.

Border Patrol welcomes potential upgrade

A border patrol officer stands next to some of U.S. President Donald Trump's eight border wall prototypes as they near completion along U.S.- Mexico border in San Diego, California. Mike Blake | Reuters

The U.S. Congress has so far shown little interest in appropriating the estimated $21.6 billion it would cost to build the wall. Still, border patrol officials on Monday welcomed the momentum on Trump's pledge, which generated a groundswell of voter support that helped elect him to office. "Our current infrastructure is well over two decades old," Roy Villareal, deputy chief patrol agent of the U.S. Border Patrol's San Diego sector, said during a tour with media organizations on Monday morning. "Is there need for improvement? Absolutely."

Replacement fence long overdue

A worker chats with residents at a section of the U.S. - Mexico border fence at Sunland Park, U.S., opposite the Mexican city of Ciudad Juarez, Mexico January 26, 2017. Jose Luis Gonzalez | Reuters

Currently, 654 miles of the 1,900-mile border with Mexico is fenced, with single, double or triple fences. The second line of fencing in San Diego, about 18 feet tall, has been breached nearly 2,000 times in the last three years, Villareal said. Even if Trump's wall never gets funded, Villareal said, the border patrol might incorporate one or more of the new wall designs as it replaces worn sections of the existing fence.

Wall aesthetics

Three of U.S. President Donald Trump's eight border wall prototypes are shown near completion along U.S.- Mexico border in San Diego, California, U.S., October 23, 2017. Mike Blake | Reuters

Six contractors from across the country were selected to build the eight prototypes, all of which will be completed this week. The builders paid attention to aesthetics in their bid to win lucrative contracts. One wall segment features deep-blue steel and another has a brick facade, standing in sharp contrast to the area's existing border fence, a ramshackle structure of corrugated steel left over from the Vietnam War.

Testing the walls

Federal agents stand watch over U.S. President Donald Trump's eight border wall prototypes as they near completion along U.S.- Mexico border near San Diego, California, U.S., October 23, 2017. Mike Blake | Reuters

In late November, a private company, which border patrol officials declined to name, will begin a 30- to 60-day process of testing the wall prototypes to determine how easy they would be to climb over or dig beneath. The final selection could be a combination of the prototype designs, Villareal said.

Concrete view

A prototype for U.S. President Donald Trump's border wall with Mexico is seen in this picture taken from the Mexican side of the border in Tijuana, Mexico October 12, 2017. Jorge Duenes | Reuters

While solid, concrete walls have a daunting presence, they might have an adverse effect on some border patrol activities, since agents would not be able to see potential crossers approaching the wall. "It's not so much the size of the wall, it's the ability to see whether it's 10 people or 30 people with ... rifles," said Rowdy Adams, a former border patrol agent who left the agency in 2011 after 30 years. "It's important to see that and set your response plan in place."

The fence-wall

Five of U.S. President Donald Trump's eight border wall prototypes are shown near completion along U.S.- Mexico border near San Diego, California, U.S., October 23, 2017. Mike Blake | Reuters

Two of the eight prototypes have a see-through design. Environmentalists have warned that a solid wall would prevent wildlife, including a dwindling population of federally protected ocelots, from crossing.

Concrete boycott

A prototype for U.S. President Donald Trump's border wall with Mexico is seen in this picture taken from the Mexican side of the border in Tijuana, Mexico October 12, 2017. Jorge Duenes | Reuters

A concrete wall may also prove challenging to build without participation from some of the world's largest concrete suppliers. Mexico's Cemex and Switzerland's LafargeHolcim told Reuters they were not participating in projects associated with the wall.

And the winner is...yet to be determined.