The Rhine-Danube frontier was established, fixing boundaries between the Roman Empire and European tribes to the north.

The Rhine-Danube frontier was mostly established between 15 b.c.e. and 15 c.e. through the determination of Augustus (earlier known as Octavian) to limit the boundaries of the immense empire of which he was the first emperor (princeps). Augustus
Caesar, Julius
Claudius Drusus, Nero
Tiberius
Arminius
Quinctilius Varus, Publius
Germanicus

Julius Caesar had conquered Gaul between 58 and 50 b.c.e., thereby extending Roman rule to the Rhine. In the course of his campaigns against the Celts and the Germans who had come into eastern Gaul, Caesar came to realize the value of the Rhine as a frontier. To coerce the Germans into similar respect for this natural boundary, Caesar built a temporary wooden bridge, crossed the river in 55 b.c.e., conducted extensive raids in German lands for two weeks, and then returned to Roman territory. His intimidating campaign had the effect of keeping the Germans away from Gaul for thirty years, though there was no true frontier.

Gaul (with the Rhine valley) was one of the “imperial” provinces assigned to Augustus from the start of the Roman Empire in 27 b.c.e. His enormous powers allowed him to create Rome’s first unified frontier policy. Equally advantageous, all newly created provinces were automatically designated “imperial.” Governors of imperial provinces were styled “propraetorian legates of the emperor” (legati propraetore Augusti); the emperor was commander in chief, possessed proconsular imperium, and delegated imperium to his appointees.

At the opening of Augustus’s reign, Rome had extensive possessions in the west and the east but lacked control of the Alps and the Balkan peninsula. Northern Italy, Illyricum, and Macedonia could not be defended against serious attack by barbarian tribes. Augustus determined to expand Roman holdings up to the Danube and perhaps beyond. There were three theaters of campaigns. In the first theater, Augustus sent legions under the command of his capable stepsons Tiberius and Nero Claudius Drusus through the Alps to the upper Danube region in 16 b.c.e., while he himself took charge in Gaul. Within two years, Tiberius and Drusus were largely done. A legion soon occupied Vindonissa (now Windisch, on the Aare near Brugg). Modern Switzerland, southern Bavaria, and western Austria became the province of Raetia. Rome annexed Noricum (now in central Austria) and administered it through prefects (praefecti) headquartered at the natives’ mountaintop commercial center, the Magdalensberg. Later, in 40-49 c.e., Claudius converted Noricum into a procuratorial province, so called because the governor was an equestrian procurator (not a senator), and moved the capital to Virunum (now Waisenberg, near Klagenfurt).

Campaigns in the second theater, south of the middle Danube, proved difficult. Augustus’s son-in-law Marcus Vipsanius Agrippa was to have directed operations but died in 12 b.c.e. Tiberius took over and had apparently completed the war by 9 b.c.e. Other generals extended Roman control over the lower Danube (modern Bulgaria) to create the province of Moesia and to reduce Thrace to a client state. The Pannonians, however, rose in an extensive revolt in 6 c.e., and Tiberius, assisted by several senior commanders, took three years to crush the uprising. Illyricum was divided into two imperial provinces: Pannonia, centering on the Drava and Sava River valleys to their confluence with the Danube, and Dalmatia, in the Balkan peninsula north of Macedonia. These conquests brought Roman rule to the western coast of the Black Sea. Fortifications were established along the Danube and probably in the tributaries to its south. The location of many legionary fortresses in the early Roman Empire remains uncertain, although bases at Emona (Ljubljana) and Poetovio (Ptuj) are probable. Dalmatia had two legions: one at Burnum on the Krka and the other at Tilurium (Gardun) on the Cetina.

Meanwhile, Drusus had marched northward from Raetia along the Rhine to establish the third theater of the campaign. Because the German tribes had renewed attacks on Gaul, it was decided to invade Germany again and push back the German frontier to the Elbe (less probably as far as the Vistula). The plan was to shorten Rome’s northern frontier by some three hundred miles and also to put Gaul beyond the reach of German attacks. Drusus entered the German heartland in 12 b.c.e., planting Roman eagles on the Elbe after fortifying the lower Rhine. He was accidentally killed in 9 b.c.e., and his brother Tiberius replaced him.

Arminius consults a prophetess.

(F. R. Niglutsch)

Rome overran but never really organized the lands east of the Rhine. The Germans revolted, and under Arminius, a young chieftain who had served with the Romans as an auxiliary commander and won Roman citizenship, they annihilated some twenty thousand Romans belonging to three legions under the command of Publius Quinctilius Varus in the famous Battle of Teutoburg Forest in 9 c.e. The site of the battle was located in the Lippe Valley. The elderly Augustus was severely shaken when news of the disaster reached him, and though Drusus’s son Germanicus undertook some punitive action and restored Roman prestige in 14-17 c.e., Rome made no further effort to encompass or restrain the Germanic tribes. They remained outside the mainstream of Roman civilization.

In the early Roman Empire, the Rhine commands were among the most important in the empire, and senators of consular rank held them. Two military districts, called Upper and Lower Germany (Germania Superior and Inferior), stretched along the Rhine; they became provinces only in 90 c.e. with capitals at Moguntiacum (modern Mainz) for Superior and Colonia Agrippinensis (modern Cologne or Köln) for Inferior. Each legate commanded four legions plus auxiliary troops. By the early second century, the garrison was reduced to just four. Other legionary fortresses along the Rhine are also the origins of modern cities: Argentorate (Strasbourg), Bonna (Bonn), Novaesium (Neuss), and Castra Vetera (Xanten). Another base was converted into a civilian colony in 49 c.e., as Colonia Claudia Ara Agrippinsium. In the 70’s and early 80’s, Rome occupied the Black Forest area between the Upper Rhine and Upper Danube, a noticeable shortening of the frontier. By the early second century, these garrisons had been reduced to two legions each, plus auxiliaries, as the Danube became the military center of the empire.

The Danube area had been pacified after the fall of Maroboduus as king of the Marcomanni in 19 c.e., but slowly it came to have the empire’s largest concentration of forces. The bases in the Balkans were closed and their legions transferred to the Danube from Dalmatia, from the Rhine army, and even from Britain. Augusta Regina (Regensburg), Vindobona (Vienna), Aquincum (Budapest), and Singidunum (Belgrade) are legionary fortresses that have become modern cities. Trajan conquered Dacia (roughly Romania) in 101-106; his famous column in Rome commemorates the war. Ironically, it was the Marcomanni who (with the Quadi) in the reign of Marcus Aurelius (r. 161-180 c.e.) first seriously challenged the frontier after two centuries of the Pax Romana. Rome’s ultimate establishment of the Rhine-Danube line as its northern frontier, the subsequent Dacian conquest notwithstanding, was not a matter of choice but of necessity. Rome’s inability to conquer further was dictated by spreading internal weaknesses and revolts, the generally troublesome Parthian frontier, and the strength of Rome’s German adversaries. The establishment of the northern frontier entailed much more than the mere definition of a border; it represented both the height and the eclipse of Roman imperialism in Europe and therefore the spread of Romanitas as well.

• Alföldy, Geza. Noricum. Translated by Anthony Birley. London: Routledge & Kegan Paul, 1974. Part of Routledge’s History of the Provinces of the Roman Empire series, this work is detailed and archaeological, and its scholarship is superb.
• Drinkwater, J. Roman Gaul. London: Croom Helm, 1983. Provides an overview of activities on the Rhine frontier.
• King, Anthony. Roman Gaul and Germany. Berkeley: University of California Press, 1990. King also treats the Rhine frontier. When compared to the work of Drinkwater, cited above, King’s volume is more accessible for beginners.
• Luttwak, E. The Grand Strategy of the Roman Empire. Baltimore: The Johns Hopkins University Press, 1976. An analyst for the Department of Defense rather than an ancient historian, Luttwak has stimulated considerable debate; many doubt Rome had a “grand strategy.”
• Mocsy, A. Pannonia and Upper Moesia. London: Routledge & Kegan Paul, 1974. Like the work by Alföldy, cited above, this well-written volume is part of Routledge’s History of the Provinces of the Roman Empire.
• Syme, Ronald. “The Northern Frontier Under Augustus.” In Cambridge Ancient History, Vol. 10, edited by S. A. Cook et al. New York: Cambridge University Press, 1934. Syme’s study remains irreplaceable; archaeological work has provided some new information.
• Wilkes, J. Dalmatia. London: Routledge & Kegan Paul, 1969. Yet another superb entry in Routledge’s History of the Provinces of the Roman Empire series.
• Woolf, Greg. Becoming Roman: The Origins of Provincial Civilization in Gaul. New York: Cambridge University Press, 1998. An examination of the relationship between the Roman Empire and Gaul. Bibliography and index.

Arminius; Augustus; Julius Caesar; Tiberius. Rhine-Danube frontier