<P> The Vandals conquered Sicily, and their fleet became a constant danger to Roman sea trade and to the coasts and islands of the western Mediterranean . </P> <P> Avitus, at the Visigothic court in Burdigala, declared himself Emperor . He moved on Rome with Visigothic support which gained his acceptance by Majorian and Ricimer, commanders of the remaining army of Italy . This was the first time that a barbarian kingdom had played a key role in the imperial succession . Avitus's son - in - law Sidonius wrote propaganda to present the Visigothic king Theoderic II as a reasonable man with whom a Roman regime could do business . Theoderic's payoff included precious metal from stripping the remaining public ornaments of Italy, and an unsupervised campaign in Hispania . There he not only defeated the Sueves, executing his brother - in - law Rechiar, but he also plundered Roman cities . The Burgundians expanded their kingdom in the Rhone valley and the Vandals took the remains of the Diocese of Africa . In 456 the Visigothic army was too heavily engaged in Hispania to be an effective threat to Italy, and Ricimer had just destroyed a pirate fleet of sixty Vandal ships; Majorian and Ricimer marched against Avitus and defeated him near Placentia . He was forced to become Bishop of Placentia, and died (possibly murdered) a few weeks later . </P> <P> Majorian and Ricimer were now in control of Italy . Ricimer was the son of a Suevic king and his mother was the daughter of a Gothic one, so he could not aspire to an imperial throne . After some months, allowing for negotiation with the new emperor of Constantinople and the defeat of 900 Alamannic invaders of Italy by one of his subordinates, Majorian was acclaimed as Augustus . Majorian is described by Gibbon as "a great and heroic character". He rebuilt the army and navy of Italy with vigour and set about recovering the remaining Gallic provinces, which had not recognized his elevation . He defeated the Visigoths at the Battle of Arelate, reducing them to federate status and obliging them to give up their claims in Hispania; he moved on to subdue the Burgundians, the Gallo - Romans around Lugdunum (who were granted tax concessions and whose senior officials were appointed from their own ranks) and the Suevi and Bagaudae in Hispania . Marcellinus, magister militum in Dalmatia and the pagan general of a well - equipped army, acknowledged him as emperor and recovered Sicily from the Vandals . Aegidius also acknowledged Majorian and took effective charge of northern Gaul . (Aegidius may also have used the title "King of the Franks".) Abuses in tax collection were reformed and the city councils were strengthened, both actions necessary to rebuild the strength of the Empire but disadvantageous to the richest aristocrats . Majorian prepared a fleet at Carthago Nova for the essential reconquest of the Diocese of Africa . </P> <P> The fleet was burned by traitors, and Majorian made peace with the Vandals and returned to Italy . Here Ricimer met him, arrested him, and executed him five days later . Marcellinus in Dalmatia, and Aegidius around Soissons in northern Gaul, rejected both Ricimer and his puppets and maintained some version of Roman rule in their areas . Ricimer later ceded Narbo and its hinterland to the Visigoths for their help against Aegidius; this made it impossible for Roman armies to march from Italy to Hispania . Ricimer was then the effective ruler of Italy (but little else) for several years . From 461 to 465 the pious Italian aristocrat Libius Severus reigned . There is no record of anything significant that he even tried to achieve, he was never acknowledged by the East whose help Ricimer needed, and he died conveniently in 465 . </P>

What was the main reason for the decline of the roman empire