 The U.S.'s First Transcontinental Railroad was built between 1863 and 1869 to join the eastern and western halves of the United States.Begun just before the American Civil War, its construction was considered to be one of the greatest American technological feats of the 19th century.Known as the "Pacific Railroad" when it opened, this served as a vital link for trade, commerce, and travel and opened up vast regions of the North American heartland for settlement.