Honorius  (September 384 – 15 August 423) 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.
Honorius died of edema on 15 August 423, leaving no heir.[22] In the subsequent interregnum Joannes was nominated Emperor. The following year, however, the Eastern Emperor Theodosius II installed his cousin Valentinian III, son of Galla Placidia and Constantius III, as Emperor.
 
The Mausoleum of Honorius was located on the Vatican Hill, accessed from the transept of the Old Saint Peter's Basilica. It was first used for Maria. Probably Thermantia and Honorius's sister Galla Placidia, and perhaps other imperial family members, were later buried there. In the 8th century it was transformed into a church, the Chapel of St Petronilla, which held the relics of the saint and was demolished when the New St Peter's was erected.