Constantine III, a general of obscure origins but considerable talent, was proclaimed emperor in Britain in 407 by his soldiers following the assassinations of the usurpers Marcus and Gratianus (neither of whom issued coins). He led his troops across the Channel into Gaul, where his authority was swiftly accepted locally, but was opposed by the reigning Western emperor Honorius, who sent his general Sarus from Italy to harass his defences. After initial setbacks, Constantine gained the upper hand and occupied all of Gaul up to the Alps, establishing his base at Arles. At its greatest extent, the territories controlled by Constantine included all of Western Europe, from Britain in the North and Spain in the South. Soon, however, his grip began to loosen. First Britain rose in revolt, and then Gerontius, Constantine's own magister militum, whom he had sent to Spain to quell another revolt, ended up turning against him. His fate was sealed in 411 when Honorius sent a general by the name of Constantius (the future emperor Constantius III) to defeat him. Although he had taken refuge in a church and was ordained before surrendering, the former rebel was murdered in captivity and his head sent to Ravenna where it was exhibited for some time.