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.
Constitutional reforms of Julius Caesar
After Caesar's assassination, Mark Antony, who at the time had been Caesar's fellow consul, eventually formed an alliance with Caesar's adopted son and great-nephew, Gaius Octavian. Along with Marcus Aemilius Lepidus, who was Caesar's magister equitum (master of horse) at the time of his assassination, they formed an alliance known as the Second Triumvirate. They held powers that were nearly identical to the powers that Caesar had held under his constitution, and as such, the senate and assemblies remained powerless. The conspirators were defeated at the Battle of Philippi in 42 BC. Lepidus became powerless, and Antony went to Egypt to seek glory in the east, while Octavian remained in Rome. Eventually, however, Antony and Octavian fought against each other in one last battle. Antony was defeated in the naval Battle of Actium in 31 BC, and committed suicide in 30 BC. In 29 BC, Octavian returned to Rome, as the unchallenged master of the state. In 27 BC, Octavian offered to give up the Dictatorial powers which he had held since 42 BC, but the senate refused, and thus ratified his status as master of the state. He became the first Roman Emperor, Augustus, and the transition from Roman Republic to Roman Empire was complete.