Casperius Aelianus, who served as Praetorian Prefect under the emperors Domitian and Nerva, was a Praetorian Prefect loyal to the Roman Emperor Domitian, the last of the Flavian dynasty. After Domitian's murder and the ascension of the Emperor Nerva, Aelianus laid siege to the Imperial Capital in order to force the capture of the men responsible for Domitian's death, who had not been punished by Nerva. Aelianus succeeded in his demands, greatly weakening the authority of the Emperor, so much so that Nerva realized that his position was no longer tenable without the support of an heir who had the approval of the Roman army. Within two or three months Nerva announced the adoption of the highly respected general Trajan as his successor, and with this decision all but abdicated.