US President Donald Trump signed on Wednesday an executive order to start the Mexico border wall project at the Department of Homeland Security facility in Washington, DC. /CFP Photo

The aim of the wall is to keep out immigrants from Mexico. Trump seems to be making good on a pledge he made on the campaign trail in June 2015. /CFP Photo

The border-long wall, which stretches over 3,110 kilometers, could be one of the most costly US state projects ever. /CFP Photo