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
Under Augustus, the European borders of the empire he inherited from his grand-uncle Julius Caesar were considerably expanded. During the first half of his sole rule (30–9 BC), Augustus' central strategic objective was to advance the Roman border from Illyricum and Macedonia to the line of the Danube, Europe's greatest river, in order both to increase strategic depth between the border and Italy and to provide a major fluvial supply route for the Roman armies in the region. The strategy was successfully executed: Moesia (29-7 BC), Noricum (16 BC), Raetia (15 BC) and Pannonia (12-9 BC) were annexed in steady succession. After settling the Danube border, Augustus turned his attention to the North, where Julius Caesar had in 51 BC established the border of Roman Gaul along the river Rhine, the second major European fluvial route. Augustus launched an ambitious strategy of advancing the Rhine border to the river Elbe, aiming to incorporate all the warlike Germanic tribes. This would eliminate their chronic threat to Gaul, increase strategic depth between free Germans and Gaul, and make the western Germans' formidable manpower available to the Roman army. But a massive and sustained military effort (6 BC – AD 9) came to nothing. Roman advances in Germania Magna (i.e. Germany outside the empire) had to be scaled down during the Great Illyrian Revolt of AD 6-9, when many troops were diverted to Illyricum. Then Augustus' expansion strategy suffered a crushing setback when some 20,000 Roman troops were ambushed and massacred by the Germans at the Battle of the Teutoburg Forest in AD 9. After this, Augustus shelved his Elbe strategy. It was apparently revived briefly by his successor Tiberius, whose nephews, the generals Germanicus and Drusus, launched major and successful operations in Germania in AD 14-17, during which the main tribes responsible for Varus' defeat were crushed and the three lost legionary "aquilae" (eagle-standards) were recovered.