President Donald Trump has asked Congress for $1.6B in his 2018 budget for the border wall that became a central issue in his presidential campaign.

The $1.6B would build and replace 74 miles of barriers. The Department of Homeland Security’s budget asks Congress for “32 miles of new border wall construction, 28 miles of levee wall along the Rio Grande Valley and 14 miles of new border wall system that will replace existing secondary fence in the San Diego Sector.” 

Because the wall will take three and a half years to construct, according to the Department of Homeland Security, additional funds are expected to be requested in subsequent years.

The Department of Homeland Security estimated the wall, which would stretch the 1,200 miles separating the U.S. from Mexico, would cost $22B. About 650 miles of barriers exist along the border. 

In March, the Department of Homeland Security opened two requests for proposals — one for a concrete wall and another for other types of barriers — and got some pitches that included incorporating shipping containers. Mexico's president, Enrique Peña Nieto, has said his country will not pay for the proposed wall.