 Complete the following phrase:  The Nervan-Antonine dynasty ended in chaos. The senate declared damnatio memoriae on Commodus, whose urban prefect Pertinax was declared Emperor by the Praetorian Guard in return for the promise of very large donatives. Pertinax had risen through equestrian ranks by military talent and administrative efficiency to become senator, consul and finally and briefly Emperor; he was murdered by his Praetorians for attempting to cap their pay. Pertinax was replaced by Didius Julianus, who had promised cash to the Praetorians and restoration of power to the Senate. Julianus began his reign with an ill-judged appeal to the memory of Commodus, a much resented attempt to bribe the populace en masse and the use of Praetorian force against them. In protest, a defiant urban crowd occupied the senatorial seats at the Circus Maximus. Against a background of civil war among 