Augustus
Augustus' reign laid the foundations of a regime that lasted, in one form or another, for nearly fifteen hundred years through the ultimate decline of the Western Roman Empire and until the Fall of Constantinople in 1453. Both his adoptive surname, Caesar, and his title "Augustus" became the permanent titles of the rulers of the Roman Empire for fourteen centuries after his death, in use both at Old Rome and at New Rome. In many languages, "Caesar" became the word for "Emperor", as in the German "Kaiser" and in the Bulgarian and subsequently Russian "Tsar" (sometimes Csar or Czar). The cult of "Divus Augustus" continued until the state religion of the Empire was changed to Christianity in 391 by Theodosius I. Consequently, there are many excellent statues and busts of the first emperor. He had composed an account of his achievements, the "Res Gestae Divi Augusti", to be inscribed in bronze in front of his mausoleum. Copies of the text were inscribed throughout the Empire upon his death. The inscriptions in Latin featured translations in Greek beside it, and were inscribed on many public edifices, such as the temple in Ankara dubbed the "Monumentum Ancyranum", called the "queen of inscriptions" by historian Theodor Mommsen.
Roman army
During this period the Republican system of citizen-conscription was replaced by a standing professional army of mainly volunteers serving standard 20-year terms (plus 5 as reservists), although many in the service of the empire would serve as many as 30 to 40 years on active duty, as established by the first Roman emperor, Augustus (sole ruler 30 BC – AD 14).Regular annual conscription of citizens was abandoned and only decreed in emergencies (e.g. during the Illyrian revolt 6–9 AD). Under Augustus there were 28 legions, consisting almost entirely of heavy infantry, with about 5,000 men each (total 125,000). This had increased to a peak of 33 legions of about 5,500 men each (c. 180,000 men in total) by AD 200 under Septimius Severus. Legions continued to recruit Roman citizens, mainly the inhabitants of Italy and Roman colonies, until 212. Legions were flanked by the auxilia, a corps of regular troops recruited mainly from "peregrini", imperial subjects who did not hold Roman citizenship (the great majority of the empire's inhabitants until 212, when all were granted citizenship). Auxiliaries, who served a minimum term of 25 years, were also mainly volunteers, but regular conscription of "peregrini" was employed for most of the 1st century AD. The "auxilia" consisted, under Augustus, of about 250 regiments of roughly cohort size, that is, about 500 men (in total 125,000 men, or 50% of total army effectives). Under Severus the number of regiments increased to about 400, of which about 13% were double-strength (250,000 men, or 60% of total army). "Auxilia" contained heavy infantry equipped similarly to legionaries, and almost all the army's cavalry (both armoured and light), and archers and slingers.