Construction on prototypes of President Trump’s promised border wall could begin in two weeks after the administration on Thursday announced the selection of four companies tapped to build them after months of delays in the bidding process.

The U.S. Customs and Border Protection said the selection of the companies to build the concrete prototypes, which will take place in San Diego, is the first major step in fulfilling Trump’s campaign pledge to build a wall along the 2,000-mile border with Mexico.

“Today we mark a significant milestone,” said Ronald Vitiello, acting deputy commissioner of U.S. Customs and Border Protection. “This is the first tangible result of the action planning that has gone on.”

“We’re going to do this as quickly as we can while maintaining all the requirements,” he said. “We think it’s in a couple of weeks to get started.”