The Rhine frontier had remained fairly quiet. German tribes had launched raids across it in 29 and 17 B.C., but these were not in themselves sufficient to lead Augustus to change his policy, though they would afford him an excuse if he so decided. However, the general pacification that had been attained by about 13 B.C. enabled him, as already has been seen, to think of further advance. Thus when in 12 B.C. he ordered a move over the Rhine which led Roman arms to the Elbe, it is not unreasonable to suppose that he had decided upon the permanent conquest of western Germany and the substitution of an Elbe-Danube frontier for one based upon the Rhine and Danube. This task was entrusted to his stepson Drusus, who made annual thrusts eastwards beyond the Rhine and brought a fleet from the Rhine to the North Sea through a canal which he made through the lakes of Holland; he thus secured the support of the Batavians and won that of the Frisii, who in return for supplying auxiliary troops became Rome’s allies. In 11 B.C. Drusus advanced from Vetera (Xanthen) to the Visurgis (Weser), subduing the Usipetes, north of the Lippe; the next year he attacked the Chatti from his base at Moguntiacum (Mainz); in 9 B.C. he attacked the Marcomanni, advanced through the territory of the Cherusci and reached the Elbe, but he died as the result of an accident. His elder brother Tiberius was given proconsular authority and was put in control of the Tres Galliae and the Rhine armies; he carried on the task of pacification until recalled in 7. Other commanders continued to operate in the area, though on a lesser scale: for instance L. Domitius Ahenobarbus advanced from the Danube to the Elbe along the river Saale, a tributary of the Elbe; he also built a causeway (pontes longi) over marshy land between the Rhine and Ems.
In A.D. 4 Tiberius returned to the German front. In the next year his fleet and army combined in an advance to the Elbe, while some ships were despatched to explore the coast of Jutland. The stage was now set for the next big move: the conquest of the Marcomanni in Bohemia. If they were reduced the defence of the Elbe could be linked with that of the Danube, and a new frontier be established along the line of the modern cities of Hamburg, Leipzig, Prague and Vienna and thence along the Danube to the Black Sea. The Marcomanni had recently moved from the valley of the Main to Bohemia where their leader Maroboduus had built up a strong kingdom, but Roman diplomacy and arms had limited its expansion: the Hermanduri to its west and the Semnones (east of the Elbe) to its north were friendly to Rome, while the Dacians to its east (in modern Romania, north of the Danube) had recently been defeated by the Romans as a reprisal for Dacian raids. In A.D. 6 therefore Tiberius was ready to launch a great converging attack with twelve legions on Maroboduus, but as the Roman troops were advancing and the net was closing around him Maroboduus was dramatically saved. News came of the great revolt in Pannonia. Tiberius prudently broke off operations, reached an agreement with Maroboduus by which he was recognized as king and a friend of the Roman people, and hastened off to save Illyricum from disaster. This done, Tiberius was not free to give further thought to the Marcomanni since a fresh calamity in Germany demanded his presence. His military services to the Empire were indeed of a high order.
Roman armies had overrun the country from Rhine to Elbe, but the conquest had not yet been consolidated by the construction of permanent forts or roads, and regular patrolling was still needed. About 9 B.C. an altar to Roma et Augustus had been established at the tribal capital of the Ubii (later Cologne), whom Agrippa had earlier at their own request settled on the west bank of the Rhine; and in 2 B.C. Domitius had erected another altar on the Elbe. But the country between the rivers lacked cities and clearly was not yet ripe for conversion into a normal Roman province. Tribal unrest found a leader in Arminius and an opportunity in the arrival of Quinctilius Varus. Arminius, chief of the Cherusci, had obtained Roman citizenship, served in the Roman auxilia, and gained equestrian rank; he now plotted rebellion with neighbouring tribes. Varus, who had married the grandniece of Augustus, owed his appointment as legate of the Rhine armies in C´.C·. 9 to the emperor’s favour. His earlier governorship of Syria had been successful, but he appears to have misjudged conditions in his new command, where he is said to have tried to introduce unpopular methods of taxation and jurisdiction. At any rate he unsuspectingly entertained Arminius in his camp on the Visurgis and when winter approached he began to withdraw his three legions westwards to their winter quarters. But as he was marching through the dense Teutoburgian Forest, he was treacherously attacked by Arminius: the three legions were virtually annihilated and Varus committed suicide.
Tiberius hurried to the spot, and although Rome lost all east of the Rhine, there was little fear that Arminius, who failed to win the co-operation of Maroboduus, would threaten Gaul itself. With eight legions Tiberius and his nephew Germanicus, who took over the chief command in A.D. 12, successfully reorganized the defence of the river and conducted some reprisals beyond it. Had Augustus so decided, the lost ground presumably could have been recovered, but he was old and shaken: he would cry out to the spirit of the man whom he himself had appointed, ‘Quinctili Vare, legiones redde’, and he wore deep mourning on each anniversary of the clades Variana. The loss involved a serious diminution of the narrow margin of military man-power, and the standing army was reduced from twenty-eight to twenty-five legions; the moral effects might be more widespread. What policy Augustus would have adopted, if he had enjoyed the prospect of a long life before him, cannot be known, but in the circumstances he appears to have abandoned all thought of any frontier beyond the Rhine. A narrow area along the river was divided into two districts, Upper (southern) and Lower (northern) Germany, with the division near Coblenz. Each received a permanent garrison of four legions, commanded by consular military legates: they were military zones, not provinces, and their civil administration was the responsibility of the governor of Belgica. The legions were quartered in permanent camps at Vetera (Xanten; a double camp), Novaesium (Neuss), Bonna (Bonne), Moguntiacum (Mainz; double), Argentorate (Strassburg) and Vindonissa (Windisch in Switzerland).
The Varian disaster no less than the Pannonian revolt was a dark shadow, but none the less Augustus had in general achieved a lasting success. He had secured the Danube frontier by the organization of Raetia, Noricum, Pannonia and Moesia, backed by seven legions; and the Rhine was firmly held by its eight. Four in Syria, two in Egypt, one in Africa and three in Spain, aided by oceans, deserts and rivers, co-operated in holding back all assailants on those frontiers which Augustus had chosen with care and deliberation for the Empire. The pattern was complete and must not lightly be altered. In the Brevarium totius imperii, which he wrote in his own hand, he added as a final clause a piece of advice: ‘consilium coercendi intra terminos imperii’.