The Iron Legion (COMIC: Doctor Who and the Iron Legion) or Ferrum Legion (PROSE: Warlords of Utopia) was a fearsome army of robotic legionnaires (COMIC: Doctor Who and the Iron Legion, PROSE: Warlords of Utopia) in Roma D, one of the many Known Worlds where the Roman Empire never fell. The leader of Roma D committed the Ferrum Legion to the Empire of Empires' war against the Greater German Reich during the War in Heaven. (PROSE: Warlords of Utopia)

The Fourth Doctor encountered the Iron Legion when they invaded Stockbridge. By that time, the Legion was made up of veterans of "the eternal war" and, led by General Ironicus, had conquered the galaxy. They used infrared vision and could detect heartbeats with their sonar. The Iron Legion took prisoners from other dimensions to feed the Malevilus as offerings. When the Fourth Doctor escaped into their reality, he programmed the Bestiarus to start a revolution by attacking the Iron Legion at key points throughout Rome. (COMIC: Doctor Who and the Iron Legion)

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