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 Emperor (Principate)
A far more important development was the "Second Settlement" of 23 BC, when Caesar Augustus accepted "tribunicia potestas" for life and "imperium maius proconsulare". Two further developments concluded the establishment of the Imperial dignity: Caesar Augustus accepted "imperium consulare" on an "ad personam" basis in 19 BC and was elected "pontifex maximus" in 13 BC. Thus the Imperial dignity was fully established as the extraordinary concentration of ordinary powers and immunities."Caesar Augustuss third wife Livia Drusilla (subsequently "Julia Augusta") had previously borne two children by her first husband, Tiberius Claudius Nero: Tiberius and Drusus. Tiberius's second wife was Julia the Elder, Marcus Agrippa's widow (his first wife had been Vipsania, Agrippa's daughter by his first marriage); Caesar Augustus adopted Tiberius on June 26, 4, whereupon Tiberius himself adopted his brother Drusus's son by Mark Antony's daughter who was also Augustus' niece, Germanicus Julius Caesar. Germanicus married Vipsania Agrippina, Agrippa's daughter by Julia and Tiberius's stepdaughter, and had by her one surviving son, Gaius "Caligula" ("Little Boots"), and a daughter, Julia Agrippina, whose third husband was Germanicus's brother by blood, Claudius (she was his fourth wife); Agrippina had already borne a son, Lucius, whom Claudius adopted under the name Nero"' in 40; Nero married Claudius's daughter Claudia Octavia in 53.