Quick Answer: The Dominate was a period traditionally used to describe the Roman Empire beginning with the reign of Emperor Diocletian. The term Dominate is now rarely used as an analytical model in modern scholarship. Proposed in the 19th-century by the German scholar Theodor Mommsen, he contrasted it with the earlier Principate established by Augustus in 27 BC, which he interpreted as a system in which imperial authority was formally embedded within Roman Republican institutions. Mommsen argued that this later period marked a rupture in the constitutional basis of the empire, moving from one legitimised by a republican senate and people to one where the emperor became the state. Since the start of the 20th century, scholars have increasingly rejected this view of a rupture around the time of Diocletian.