Emilio Mola, a Nationalist general during the Spanish Civil War, told a journalist in 1936 that as his four columns of troops approached Madrid, a "fifth column" () of supporters inside the city would support him and undermine the Republican government from within [REF].
Some writers, mindful of the origin of the phrase, use it only in reference to military operations rather than the broader and less well defined range of activities that sympathizers might engage in to support an anticipated attack.