7-09. How the Rhine Became the Frontier of Empire

One of the first acts of Commodus, an unworthy successor of his father, was to make peace which surrendered to the all but beaten enemy every advantage that had been wrested from them The struggle for the lands to the north of the Danube was at an end. Meanwhile the Romans were confronted, about the close of the century, with a new and dangerous enemy in the west, in the angle between the Main and the frontier of upper Germany and Rhaetia — by the Alemans. As their name indicates, the Alemans were not a single tribe but a union of tribes — a confederacy.

We hear (somewhat later) the names of several of the component tribes, the Juthungi, the Brisigavi, the Bucinobantes, and the Lentienses.

Whence did they come? No doubt the nucleus of this confederacy was formed by the southern divisions of the Hermunduri. To these there may have attached themselves various fragments of peoples which had split off before and after the Marcomannic war, just as later, towards the middle of the third century, the Semnones, in the course of a migration southward, probably joined this confederacy and were absorbed by it.

Before long — as early as 213 — the new nation came in contact with the Romans. So far as can be made out from the confused account which is given us of their first appearance they had invaded Rhaetia, whereupon the Emperor Caracalla took the field against them, flung them back across the frontier and advanced into their territory carrying all before him. Before twenty years had passed the Teutons— presumably the Alemans again — renewed the attack upon the Roman frontier defences.

So threatening was the situation that the Emperor Severus Alexander felt himself obliged to break off his campaign against the Persians, and take over in person the direction of the operations on the Rhine. Negotiations had already begun before his assassination in March 235, but his successor, the rough and soldierly Maximin, brought new life into the campaign. Advancing by forced marches into the country of the Alemans he drove the barbarians before him without serious resistance, laid waste their fields and dwellings far and wide, and finally defeated them far in the interior of their territory.

The result of this campaign, the last war of offence on a large scale which the Romans waged on the Rhine, was the restoration of security to the frontier for a period of twenty years. Under Gallienus — probably about the year 258 — the storm broke. With irresistible force the armies of the Alemans broke through the great chain of frontier fortifications between the Main and the Danube, and after overpowering the scattered Roman garrisons, poured like a flood across the whole of the Agri Decumates, and established themselves permanently in the conquered territory. At the same time Rhaetia became a prey to them; nay more, a strong force even crossed the Alps and penetrated as far as Ravenna. The invaders were, it is true, defeated by Gallienus near Milan, and forced to retreat, but the country at the northern base of the Alps was lost, and its loss threw open to the Germanic hordes the gates of Italy.

In addition to the Alemans of the upper Rhine, there now appeared, on the lower course of that river, another dangerous enemy, namely the Franks. The frontier had scarcely ever been seriously threatened at this point since the days of Augustus, but now under Gallienus the situation was altered. Here also there had quietly grown up a confederacy which, under the name of Franci, the Free, presumably comprised the tribes formerly met with in these regions, the Chamavi, Sugambri, and other smaller clans. Their name, first heard in the time of Gallienus, was soon to become even more terrible in the ears of the Romans than that of the Alemans. The first attack of the new league of peoples upon the Rhine frontier occurred in 253. The districts on the Gaulish bank of the Rhine soon fell into the hands of the enemy. With great difficulty Gallienus succeeded in forcing them back across the Rhine. But others followed them, and there ensued a series of desperate struggles which lasted till 258. On the whole the Romans had the best of it, even though their army was not large enough to prevent isolated bands of Franks from establishing themselves upon the left bank of the Rhine.

In 258 Gallienus was called away to the lower Danube, which urgently demanded his presence. The confusion which was created in the Rhine district by the assassination in the following year of the Emperor's son Valerian who had been left behind as Imperial Resident at Cologne, by the ambitious general Cassianus Postumus, gave the Franks a welcome opportunity to make a new inroad into Gaul. Their bands ranged almost unresisted through the whole country from the Rhine to the Pyrenees, devastating as they went. Then they pushed on, as the Cimbri had done before them, across the mountains into Spain, and made havoc of that country for several years, reducing to subjection even great cities like Tarraco, while, like the Vandals after them, they also made a foray into Africa. As at the time of the Cimbrian war, the terror of the Germans spread through all the countries of Western Europe. Only after a considerable time Postumus — a capable soldier and a well-intentioned administrator — was able to force the Germanic hordes out of Gaul and restore peace and security. But the Rhine became the frontier of the Empire and remained so as long as the Empire lasted.

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