The Department of Homeland Security awarded four contracts for border wall prototypes, another crucial step in President Donald Trump's plan to secure the border. Officials of Customs and Border Protection gave contracts to Texas Sterling Construction of Houston, Caddell Construction of Montgomery, Alabama, Fisher Industries of Tempe, Arizona, and W.G. Yates & Sons Construction of Philadelphia.

The four companies all proposed concrete walls, NBC News reports. DHS has not yet announced contracts for companies that have proposed other types of barriers. The prototypes will be between 18 and 30 feet high and construction is expected to begin in the fall.

Once all contracts are awarded, the winning companies will have up to 30 days to build their prototypes along the border in the San Diego area. The prototype phase is expected to cost $20M.

The process was slowed by internal issues and a protest filed by a company that did not receive a contract.

"This is the first tangible result of the action planning that has gone on," Acting Deputy Commissioner of the U.S. Customs and Border Protection Ronald Vitiello said during the announcement.