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.
Imperial Roman army
Unlike the Republican legions, which were, in theory at least, temporary citizen-levies for the duration of particular wars, Augustus and his right-hand man Agrippa clearly envisioned their legions as permanent units composed of career professionals. Under the late Republic, a Roman citizen "iunior" (i.e. male of military age: 16–46 years) could legally be required to serve a maximum of sixteen years in the legions and a maximum of six years consecutively. The average number of years served was about ten. In 13 BC, Augustus decreed sixteen years as the "standard" term of service for legionary recruits, with a further four years as reservists ("evocati"). In AD 5, the standard term was increased to twenty years plus five years in the reserves. In the period following its introduction, the new term was deeply unpopular with the troops. On Augustus' death in AD 14, the legions stationed on the rivers Rhine and Danube staged major mutinies, and demanded, among other things, reinstatement of a sixteen-year term. Augustus prohibited serving legionaries from marrying, a decree that remained in force for two centuries. This measure was probably prudent in the early imperial period, when most legionaries were from Italy or the Roman colonies on the Mediterranean, and were required to serve long years far from home. This could lead to disaffection if they left families behind. But from about AD 100 onwards, when most legions were based long-term in the same frontier-province and recruitment was primarily local, the prohibition of marriage became a legal encumbrance that was largely ignored. Many legionaries formed stable relationships and brought up families. Their sons, although illegitimate in Roman law and thus unable to inherit their fathers' citizenship, were nevertheless frequently admitted to legions.