It’s instructive to take a look that the events leading up to the Teutoburg debacle as a part of the bigger picture of Rome and the German tribes. Ultimately, we’ll get to the question of the impact of Teutoburg on Roman strategy and the longer term effects on Europe, but any conclusions drawn from our review depend on placing the event in the proper context.
Caesar took Gaul in the 50s B.C. and fought with the Germans at various times when they crossed the Rhine. The Germans were tough, tougher than the Gauls, and many tribes refused to be ruled. Other tribes saw the benefit of a Roman alliance and were content to operate under treaties.
At the beginning of Augustus’ reign, Gaul consisted of Cisalpine Gaul, Narbonese Gaul (also called Transalpine Gaul), and the three parts resulting from conquests by Caesar -- Aquitaine, Lugdunensis (central Gaul) and Belgica. Geographically speaking Cisalpine Gaul refers to Gaul “on this side of the Alps” while Transalpine Gaul was Gaul “on the other side of the Alps”.
The map I created below shows the relevant activities of this period.
Augustus made the decision circa 20 B.C. to protect Cisapline Gaul by securing the Alps. There had been continuing harassment of Roman couriers by Alpine tribes and communications with the north had become an ongoing concern. To solve this problem, Augustus developed a plan to push the border northward to the Danube and establish the new border on a line from Lake Constance to Vienna. After Nerva had cleared the valleys between the Italian lakes in 16-17 B.C, the way was clear for the advance to the Danube to begin. Augustus gave his two stepsons, Tiberius and Drusus, the responsibility for the taking the new territory. Tiberius was to attack in the area near Lake Constance and Drusus work his way north through the Brenner pass. Their work was complete by the end of 15 B.C. and their accomplishments celebrated by Horace.
For, with your army, brave Drusus, demolished
the Genauni, that implacable race, in more
direct retaliation, the swift
Breuni, and their defenses, established
on the formidable Alpine heights: and soon
Tiberius, the elder Nero, entered
that fierce fight, with his favorable
omens, defeating the wild Rhaetians:
it was wonderful to see with what destruction,
in contesting the war, he exhausted those minds
intent on the deaths of our freemen,
as the south wind, almost, when it troubles
Circa 12 B.C. Augustus made a further decision to move the western German border from the Rhine to the Elbe. He was uncomfortable with the gap in the Black Forest that separated the sources of the Rhine and Danube and realized that moving the western border to the east, he could eliminate that gap. The eastern advance was entrusted to Drusus who began his campaign in 11 B.C. By the end of the year he was successful in working his way to the Weser River.
In 9 B.C. Drusus moved all the way to the Elbe before his unfortunate death in a riding accident.
Tiberius was then given proconsular control of Germania and worked at reducing it until 7 B.C. In 4 B.C. he returned to Germania, reconnoitered Jutland, and advanced to the Elbe in the north. Now with the Elbe established as the border in Germania it remained to defeat the Marcomanni in Bohemia to cement the Elbe Danube connection.
But it was not to be. In the midst of the war with the Marcomanni, Tiberius was forced to treat with them and break off to put down a revolt in Pannonia (present day Hungary). The revolt was put down in 6 A.D. with the help of young Germanicus.
Now Tiberius had a couple of years to catch his breath before the Teutoburg disaster.