The Dominate, also known as the late Roman Empire, is the name sometimes given to the "despotic" later phase of imperial government in the ancient Roman Empire. It followed the earlier period known as the "Principate". Until the empire was reunited in 313, this phase is more often called the Tetrarchy. It may begin with the commencement of the reign of Diocletian in AD 284, following the Third Century Crisis of AD 235–284, and to end in the west with the fall of the Western Roman Empire in AD 476, while in the east its end is disputed, as either occurring at the close of the reign of Justinian I (AD 565) or of Heraclius (AD 641). In form, the Dominate is considered to have been more authoritarian, less collegial and more bureaucratic than the Principate from which it emerged. Etymology The modern term dominate is derived from the Latin dominus, which translates into English as lord or master. Dominus, traditionally used by Roman slaves to address their masters, was sporadically used in addressing emperors throughout the Principate, usually in the form of excessive flattery (or political invective) when referring to the emperor. Augustus actively discouraged the practice, and Tiberius in particular is said to have reviled it as sycophancy. Domitian encouraged its use, but none of the emperors used the term in any semi-official capacity until the reign of Aurelian in AD 274, where coins were issued bearing the inscription deus et dominus natus. However, it was only under Diocletian that the term dominus was adopted as part of the emperor's official titulature, forming part of Diocletian's radical reforms. Transition from the Principate The Dominate system of government emerged as a response to the 50 years of chaos that is referred to as the Crisis of the Third Century. The stresses and strains of those years (chronic usurpations, military insurrections, simultaneous military conflicts across multiple frontiers) exposed the weaknesses in the Roman state under the Principate, and saw a gradual movement from the collegiate model of government that existed prior to AD 235 to a more formally autocratic version that begins after AD 285. In broad terms, it saw the gradual exclusion of the senatorial elite from high military commands and the parallel elevation of the equestrian orders, the reorganisation of the armed forces and the creation of mobile field armies, changes in imperial dress and ceremonial displays, a