The Department of Homeland Security has selected six companies that it will award up to $2.4 billion to build four concrete and four alternative wall prototypes at the U.S.-Mexico border, according to new data from the federal government.

U.S. Customs and Border Protection announced this latest step on Thursday to carrying out President Trump's campaign promise to secure the southern border, which will start with companies building prototypes.

The companies were selected from hundreds that submitted proposals earlier this year on how to create border barriers.

Caddell Construction Company, Fisher Sand & Gravel Company, Texas Sterling Construction Company, and W.G. Yates and Sons Construction Company will each receive up to $300 million to build a solid concrete wall prototype, CBP and FBP announced Aug. 31.

Caddell and Yates, as well as KWR Construction, Inc. and ELTA North America Inc. will also be given up to $300 million each to build "alternate materials border wall prototypes," according to CBP.

"Prototypes constructed from alternate materials will serve two important ends," CBP said in a statement. "[T]hey will provide an innovative perspective in the application of new materials which will allow CBP to evaluate the potential for new wall and barrier designs to complement the current wall and barrier used along the southwest border."

The project is being funded with "reprogrammed money" taken from within CBP, and is not part of the $1.6 billion border wall funding the House of Representatives approved in June, DHS confirmed Friday to the Washington Examiner. The $1.6 billion in border wall funding has yet to pass in the Senate, and may not make it out of Congress for months, if it does at all.

All of the prototype projects will be carried out on the border and are expected to start this fall, but the non-concrete walls will conclude years before the concrete projects. Each of the eight prototypes will be between 18 and 30 feet tall, and address specific issues Border Patrol agents deal with in certain regions, such as community, geography, and wildlife concerns.

Homeland Security chose to have a number of wall types built so it they can see how border operations are carried out with different barriers.

"They're all in somewhat direct competition with each other, but it's really based on the need of the Border Patrol and the need of that border area," a DHS spokeswoman said. "There's an adage in Border Patrol, 'If you've seen one part of the border, you've seen one part of the border.'"

Trump signed the Border Security and Immigration Enforcement Improvements executive order five days after becoming president. The action called for DHS to "take steps to immediately plan, design and construct a physical wall along the southern border, using appropriate materials and technology to most effectively achieve complete operational control of the southern border."

CBP put out two requests for wall design proposals on March 17.