Honorius declared Constantius III to be his co-emperor of the Western Roman Empire. Honorius: Honorius was Roman emperor from 393 to 423. He was the younger son of emperor Theodosius I and his first wife Aelia Flaccilla. After the death of Theodosius in 395, Honorius, under the regency of Stilicho, ruled the western half of the empire while his brother Arcadius ruled the eastern half. His reign over the Western Roman Empire was precarious and chaotic. In 410, Rome was sacked for the first time since the Battle of the Allia almost 800 years prior. February 8, 421. Wiki link