Short answers, pulled from the story.
The Dominate is a historiographical term traditionally used to describe the Roman Empire beginning with the reign of Emperor Diocletian around AD 284. It was coined by 19th-century German scholar Theodor Mommsen to contrast the later empire with the earlier Principate established by Augustus in 27 BC. The term is now regarded by the Oxford Classical Dictionary as a near-obsolete analytical concept.
Theodor Mommsen, a German scholar, proposed the term in the 19th century. He developed the concept in lectures delivered between 1882 and 1886, recorded by Sebastian and Paul Hensen and later published posthumously as part of his History of Rome.
Mommsen argued that the Principate, established by Augustus in 27 BC, embedded imperial authority within Roman Republican institutions, while the Dominate represented a rupture in which the emperor became the state itself. Modern scholars have largely rejected this sharp distinction, arguing that no genuine constitutional transformation separates the two periods.
Dominus originally meant "lord" and had been used to denote slave-owners. It gradually came to be applied to Roman emperors alongside the word deus, appearing on coins from the reign of Aurelian with the inscription domino et deo nato, meaning "born to be lord and god." The title was not officially adopted by emperors until the era of Constantine.
Scholars including Jochen Bleicken argued in 1978 that the Principate-Dominate division rests on no genuine constitutional transformation, and that Mommsen's view reflected 18th-19th century reactions to absolutist rule in post-Napoleonic Europe more than Roman political realities. Marketa Melounova's analysis of judicial trials found little substantive difference between the two periods, and Ronald Syme's work from the 1910s-1930s shifted focus from legal frameworks to networks of people.
Diocletian introduced the practice of genuflection, replacing the earlier custom of greeting the emperor with a handshake or kiss. Mommsen interpreted this as a move toward what he called the oriental idea, shaped by comparisons with Persian and other eastern courts. The practice reportedly aroused opposition in Rome.