Emperor Constantine III was a Roman emperor who ruled briefly in the early 5th century. He was proclaimed emperor in 407 AD by his troops in Britain, during a time of political instability in the Western Roman Empire. His reign was marked by attempts to assert control over the territories in Britain and Gaul. Constantine III's rule was short-lived, as he faced challenges from rival claimants and external threats. In 411 AD, he was defeated by the forces of Honorius, the legitimate emperor of the Western Roman Empire, leading to his capture and execution. His reign is often seen as part of the larger decline of the Western Roman Empire.