The time of the Soldier Emperors (235-284/85) is considered as a time of crisis, many historians speak of the crisis of the third century. The ongoing, forcibly brought about change on the Imperial throne did not allow the Roman Empire to get some peace.
Moreover, it had to defend itself at various fronts against new, powerful enemies: the Persian Sassanids in the east, the Goths and the Sarmatians at the Danube, and the Alamanni and Franks at the Rhine.
Around 250, Roman sources mention raids of the “Francii” into Gaul. Again and again, Franks and Alamanni raided Germania Superior, plundered the country and burnt down many forts along the Limes. The Franks, “the free ones” in their language, “the wild ones” from Roman view, were a young, large unit of Germancis into which different Germanic tribes on the right bank of the Rhine had melted: Usipetes, Tencteri, Sugambri, Bructeri and others. Also the Alamanni, “all men”, were not a tribe in the sense of an ethnical unit either, but a large unit of Germanics.
The raids increased as the Roman soldiers often came too late, and they were devastating for the Roman-Germanic provinces at the Rhine and Danube. Back then, most Roman cities did not have a city wall. Colonia Claudia Ara Agrippinensium (Cologne) was an exception, since the middle of the first century it was protected by the thick wall in which stones from the Drachenfels had been used. People in the villages, however, had no protection, so many left and moved into the interior of the Roman Empire. Villages were abandoned, and eventually large regions were deserted.
When the Sassanids attacked the Roman provinces in the east, troops from the Rhine were withdrawn and the Rhine border was hardly protected. In 256-258, the Franks invaded the province Germania Inferior. Several garrisons along the Rhine were destroyed, Trier was conquered and only Cologne with its city wall made of stone overcame the assault. Emperor Gallienus (253-268) re-conquered Trier and defended Gallia Belgica and Germania Superior. His governor in Germania Inferior, Postumus, marched against the Franks and could achieve a decisive victory. But in 260, Gallienus had to suddenly break off the campaign. His co-emperor in the east, his father Valerian, had been defeated by the Sassanid Persians and had been taken prisoner. As soon as the news reached Rome, a civil war broke out. Gallienus withdrew troops from the Rhine. Again, the Franks and Alamanni crossed the Rhine, and all Roman forts, watchtowers and civil settlements along the Limes from the Rhine to the Danube were destroyed or abandoned, and the provinces were raided heavier than ever before.
The three Gallic provinces, Germania Inferior and Germania Superior, occasionally also Spain and Britannia, seceded from Rome and grouped together into a Gallic Empire (260-274, “Imperium Galliarum”). Postumus was proclaimed emperor by his troops; he conquered Colonia Claudia Ara Agrippinensium (Cologne) and made it the capital of the new empire. Altogether, it was a good time for Gaul and the Rhineland, and another period of prosperity for CCAA, from which high-quality gold coins with Postumus’ portrait have remained. Finally Emperor Aurelian (270-275) in Rome wanted to do away with the Galllic Empire and marched over the Alps with his troops. In 274, at Châlons-sur-Marne, Aurelian defeated the Gallic emperor Tetricus and restored Rome’s authority. Yet, many soldiers had been killed, and there was almost no one left to defend the Rhine border against the Germanic intruders.
The Limes falls
Still in the same year, Frankish and Alamanni warriors crossed the Rhine and devastated the country. Agri Decumates, the land between the Rhine and the Danube, had to be given up by the romanized population. Many forts along the Rhine were destroyed, Cologne and Trier were conquered and plundered. Also large parts of today’s Netherlands, Belgium and France were devastated, Paris went up in flames. The garrison in Bonn had not been destroyed, but the villages and settlements outside were given up and the remaining civilians took cover in the garrisons. For three years, anarchy prevailed until emperor Probus (276-282) could defeat the Alamanni and the Franks. Then he made a far-reaching decision: the border of the Roman Empire was taken back to the rivers Rhine and the Danube, the Limes and the Agri Decumates were given up. At the same time, he made the Franks and Alamanni Roman allies (foederati): they were allowed to settle in Roman territory or directly at the border, in turn they had to stand loyally to the Empire and defend it if necessary. Franks settled the deserted areas on the left bank of the Rhine, and for decades things remained calm at the border.
At the end of the third century, a strong ruler ascended to the throne: Diocletian (284-305). In order to better rule the enormous empire, he split in into an eastern and a western half and appointed a co-emperor, and both emperors appointed an army leader as junior emperor (tetrarchy). The western junior emperor ruled in today’s Trier (Augusta Treverorum), so almost at the Rhine border. Diocletian re-arranged the Roman provinces. Germania Inferior remained to a large extent the same, only its name was changed into Germania Secunda, Germania Superior was split up.
Yet, the four men rule did not last for long. Already emperor Constantine (306-337) prevailed in a bloody struggle for power against his rival emperor. According to the legend, he owes his victory at the Milvian Bridge to the Christian God. During his reign, in 313, Christianity, still pursued under Diocletian, became a recognized, even privileged religion, although still no state religion. Constantine himself did not live it; like so many other emperors he was a power hungry man who had competitors killed, even in his own family. Constantine founded a new capital, Constantinople at the Bosporus, later Byzantium, today Istanbul.
The Rhine border was fortified, and also in the hinterland cavalry units were stationed. In Cologne-Deutz, around 310 the fort Deutz (castellum divitia) was built by men from the XXII. Legio Primigenia, again with stones from the Drachenfels, and the first paved Rhine bridge connected the fort with the city. At that time, about 20,000 people lived in the Roman city Colonia Claudia Ara Agrippinensium and its surroundings. Archaeologists have found proves that the region was a cosmopolite one already back then: besides the Romans and their gods there were a Christian municipality, a Jewish, and also people who believed in Isis and Mithras. Maternus (313/314) was the first bishop in our area that we know by name.
The Franks conquer Bonn and Cologne
When another bloody struggle for power broke out in the Roman Empire after Constantine’s death, the Alemanni and Franks again crossed the Rhine. Around 350, the Alemanni had brought large parts of east Gaul under their control. In 353, the Franks destroyed the garrison in Bonn, in autumn 355, they conquered and plundered Cologne. But Constantine’s nephew Julian, commander of the Gallic army, could push them back across the Rhine after violent fights (363). He re-conquered Cologne and had the garrison in Bonn reconstructed and fortified. Shortly after, he became emperor (361-363). He got the surname “the Apostate”, because he wanted to repel Christianity, yet he never had other religions prosecuted. Julian died on a campaign against the Sassanid Persians; all following emperors were Christians.
Back then, Rome permitted the Franks to settle in Toxandria, today’s Belgium. More and more Franks came, and eventually they were the largest ethnical group. It was a peaceful transition, and numerous Franks, among them the first Merovingians, served in the Roman army. The Ripuarian Franks on the right bank, however, remained enemies.
Huns and Visigoths
Since 395, the Empire was divided in a West Roman and an East Roman Empire. The Western Empire was in a constant defence fight; there was an increasing number of foreigners in its army and the commanders in chief, the army masters, were predominantly Germanics. In the 5th century they were, de facto, the mightiest men in the West Roman empire. The biggest danger for Rome loomed in the east: the Huns from Central Asia had migrated to the west, killing and destroying everyone and everything in their way. In 375, they destroyed the realm of the Ostrogoths in the south of the today’s Ukraine. The defeated people had to serve in the Hunnish army. Others fled for their lives and sought protection in the Roman Empire.
Also the Visigoths lived as allies (foederati) on Roman territory. Several times, emperor Theodosius I. fought for the throne of the Western Roman Empire, and always the Visigoth auxiliaries suffered particularly heavy casualties. When they were finally allowed to return, they found their settlements destroyed by the Huns. As they did not find peace in the East Roman Empire, and marched under their leader Alaric through the Balcans into the West Roman Empire. By 401/402, they had reached Italy. Emperor Honorius moved with his court to Ravenna which was considered impregnable. His army master Stilicho, a Vandal, could defeat the Visigoths. But already in 405/406, another army under the Goth Radagaisus invaded Italy, and still Alaric and his troops stood at the border of Italy. In this emergency situation, the Romans withdrew troops from the Rhine.
The collapse of the Rhine border
In winter 406/407, thousands of Vandals, Suebians and Alans crossed the frozen Rhine close to Mogontiacum/Mainz, overran the Franks loyal to Rome on the left bank and invaded Gaul. For long years, anarchy and great need prevailed in Gaul. Frankish crowds stormed Cologne. In 440, the city was reconquered by the Romans. In 446, the Franks again invaded. One more time the Romans could repel them, but it became obvious that Roman rule would end.
Aëtius, Attila and the battle on the Catalaunian Plains
Around 450, the King of the Huns, Attila, ruled over a giant empire stretching from the Wolga river in the east to the Rhine in the west, he was the mightiest man of the known world. On behalf of Rome, the mighty army master Flavius Aëtius (390-454). had maintained good relations with him. But then it came to a discord, and Attila took up arms. In spring 451, Hunnish troops stood at the Rhine. The Alamanni fought them, the Franks on the right bank submitted and had to serve as auxiliary troops in Attila’s army. While Aëtius summoned his armed forces together, Attila’s army penetrated into the interior of Gaul.
On the Catalaunian Plains, assumed near today’s Châlons-en-Champagne or Troyes, the two armies met one another. On both sides, partly forced coalitions faced one another.Only about half of the soldiers in Attila’s army were Huns, the other half were Ostrogoths, Gepids, Burgundians and the only recently defeated Franks from the right bank of the Rhine. In Aëtius’ army, the Visigoth provided half of the soldiers, the other half were West Romans, Franks from the left bank of the Rhine, Burgundians and Alans. Aetius and his allies defeated the Huns, and Attila withdrew from Gaul. Two years later he died, and his Empire fell apart. Aëtius did not outlive him for long, in 454 he was murdered.
The end of the Roman rule in the Rhineland
In 455, Cologne was finally sacked by Franks. The Roman rule in the Rhineland was over, and around 475, also the Latin language had disappeared. By then, the Roman Emperors had no power anymore. The last of them, Romulus Augustulus, was disposed in 476 by the Germanic military commander Odoacer.