The concept of the official portrait was established under Caesar Augustus. In the days of the Roman Republic, the numerous faces that shared the public sphere represented the swinging balance of power between factions, but when Augustus was crowned in the year 23 BC, the figure of the princeps became one with the state. Portraits of the emperor, his wife and his court were vital propaganda tools for spreading the ruler's image throughout the empire.
Sculptures were mass-produced at workshops in the capital, turning out numerous portraits of the emperor in a variety of poses: togate, thoracatus, equestrian or as the personification of various deities. These sculpted likenesses became the epicentre of civic life in the provinces, displayed as honorific statues or in shrines devoted to the imperial cult.
The style of these portraits varied over the centuries. The effigies of Augustus and his successors were marked by an idealised classicism until Nero's time, when portraits became more ornate. After the fall of the Julio-Claudian dynasty, Republican traditions were resurrected by the Flavians. With an obviously anti-elitist intention, Vespasian favoured the traditional realistic style of the middle classes. The rise of the Nerva-Antonine dynasty in the person of Trajan brought a return to the Augustan style. His successor, Hadrian, introduced a sophisticated eclecticism marked by the assimilation of Hellenic influences and took it to its logical conclusion. This process peaked during the reign of Antoninus. A baroque tendency emerged during Marcus Aurelius's rule and flourished under the Severan emperors.