The Pittsburgh-Des Moines Steel Company (originally the Des Moines Bridge and Iron Company), and often referred to as Pitt-Des Moines Steel or PDM was an American steel fabrication company. It operated from 1892 until approximately 2002 when its assets were sold to other companies, including Chicago Bridge & Iron Company.[1][2][3] The company began as a builder of steel water tanks and bridges. It also later fabricated the "forked" columns for the World Trade Center in the 1960s,[1] and was the steel fabricator and erector for the Gateway Arch in St. Louis.[4][5] A number of its works are listed on the National Register of Historic Places.[6][7]