If the government put unlimited money and supplies towards building the wall, they might get it completed in five to ten years, according to estimates by Raul Meza, state director for the Structural Engineer’s Association of Texas. Most experts agreed, however, that it would take years to complete the wall. (The existing 700 miles of fencing currently lining the border took over six years to build, according to Politifact.The U.S. Department of Homeland Security released an internal report that reveals the time-frame and cost for President Donald Trump’s intended wall along the U.S.-Mexico border: over three years to build at a cost of up to $21.6 billion.

The report eschews dealing with major physical barriers; one problem for the wall is that much of it would be privately owned or inaccessible by road. As Reuters noted, “In addition to seeking eminent domain and environmental waivers, the U.S. government would also have to meet the requirements of the International Boundary and Water Commission, a U.S.-Mexico pact over shared waters. The report estimated that agreement alone could bring the cost from $11 million per mile to $15 million per mile in one area.”

The roughly 1,250 miles wall would be completed by the end of 2020; 654 miles of the wall have already been fortified. The report that was examined by Reuters was ordered by Department of Homeland Security (DHS) Secretary John Kelly.