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.
History of the Roman Constitution
By 48 BC, after having defeated the last of his major enemies, Julius Caesar wanted to ensure that his control over the government was undisputed. He assumed these powers by increasing his own authority, and by decreasing the authority of Rome's other political institutions. Caesar held the office of Roman Dictator, and alternated between the Consulship (the chief-magistracy) and the Proconsulship (in effect, a military governorship). In 48 BC, Caesar was given the powers of a Plebeian Tribune, which made his person sacrosanct, gave him the power to veto the Senate, and allowed him to dominate the legislative process. After Caesar was assassinated in 44 BC, Mark Antony formed an alliance with Caesar's adopted son and great-nephew, Gaius Octavian. Along with Marcus Aemilius Lepidus, they formed an alliance known as the Second Triumvirate, and held powers that were nearly identical to the powers that Caesar had held under his constitution. While the conspirators who had assassinated Caesar were defeated at the Battle of Philippi in 42 BC, the peace that resulted was only temporary. Antony and Octavian fought against each other in one last battle in 31 BC. Antony was defeated, and in 30 BC he committed suicide. In 29 BC, Octavian returned to Rome as the unchallenged master of the state. The reign of Octavian, whom history remembers as Augustus, the first Roman Emperor, marked the dividing line between the Roman Republic and the Roman Empire. By the time this process was complete, Rome had completed its transition from a city-state with a network of dependencies, to the capital of an empire.