"bread and circuses" – panem et circenses) providing occasional public games, gladiators, horse races and artistic shows. Large distributions of food for the public and charitable institutions also served as popularity boosters, while the construction of public works provided paid employment for the poor. Redefinition under Vespasian With the fall of the Julio-Claudian dynasty in AD 68, the principate became more formalised under the Emperor Vespasian from AD 69 onwards. The position of princeps became a distinct entity within the broader – formally still republican – Roman constitution. While many of the same cultural and political expectations remained, the civilian aspect of the Augustan ideal of the princeps gradually gave way to the military role of the imperator. Rule was no longer a position (even notionally) extended on the basis of merit, or auctoritas, but on a firmer basis, allowing Vespasian and future emperors to designate their own heir without those heirs having to earn the position through years of success and public favor. Under the Antonine dynasty, it was the norm for the Emperor to appoint a successful and politically promising individual as his successor. In modern historical analysis, this is treated by many authors as an "ideal" situation: the individual who was most capable was promoted to the position of princeps. Of the Antonine dynasty, Edward Gibbon famously wrote that this was the happiest and most productive period in human history, and credited the system of succession as the key factor. Dominate The autocratic elements in the Principate tended to increase over time, with the style of dominus ("Lord", "Master", suggesting the citizens became servi, servants or slaves) gradually becoming current for the emperor. There was however no clear constitutional turning point, with Septimius Severus and the Severan dynasty beginning to use the terminology of the Dominate in reference to the emperor, and the various emperors and their usurpers throughout the 3rd century appealing to the people as both military dominus and political princeps. It was after the Crisis of the Third Century almost resulted in the Roman Empire's political collapse that Diocletian firmly consolidated the trend to autocracy. He replaced the one-headed principate with the Tetrarchy (c. AD 300, two Augusti ranking above two Caesares), in which the vestigial pretence of the old republican forms was largely abandoned. The title of princeps disappeared – like the territorial unity of the Empire – in favor of dominus; and