Four companies were selected to build short sections of concrete wall as models for the U.S.’s border barrier with Mexico, in the first significant step toward fulfilling President Donald Trump’s campaign promise.

U.S. Customs and Border Protection announced the four bid winners Thursday. They are Caddell Construction Co. LLC from Montgomery, Ala.; Fisher Sand & Gravel Co., doing business as Fisher Industries, in Tempe, Ariz.; Texas Sterling Construction Co. from Houston; and W.G. Yates & Sons Construction Company...