 The imperial heir Saloninus and the praetorian prefect Silvanus remained at Colonia Agrippina (Cologne), to keep the young heir out of danger and perhaps also as a check on Postumus' ambitions.Before long, however, Postumus besieged Colonia Agrippina and put the young heir and his guardian to death, making his revolt official.Postumus is thought to have established his capital here or at Augusta Treverorum (Trier), with Lugdunum (Lyon) also becoming an important city in the empire.