Constantine (died September 411, Arelate, Viennensis [now Arles, France]) was a usurping Roman emperor who was recognized as coruler by the Western emperor Honorius in 409.
Proclaimed emperor by his army in Britain in 407, Constantine crossed to the European continent with a force of British troops; by the end of the year he controlled eastern Gaul. An army dispatched by Honorius laid siege to him in Valentia (modern Valence, France) but soon withdrew. Constantine then established himself at Arelate. Joined by Roman legions from Spain, he appointed his son Constans as caesar (junior emperor) and sent him to suppress a revolt led by relatives of Honorius. After the fall (408) of Honorius’s general Stilicho, the effective ruler of the Western empire, Constantine threatened to invade Italy. Honorius was forced to recognize him as joint emperor in 409. In 411 Constantine entered Italy, but he was driven back to Arelate and besieged by Honorius’s generals. He surrendered and was executed.