The Goths were Germans coming from what is now Sweden and were followed by the Vandals, the Burgundians, and the Gepidae. The aftereffect of their march to the southeast, toward the Black Sea, was to push the Marcomanni, the Quadi, and the Sarmatians onto the Roman limes in Marcus Aurelius’ time. Their presence was brusquely revealed when they attacked the Greek towns on the Black Sea about 238. Timesitheus fought against them under Gordian III, and under Philip and Decius they besieged the towns of Moesia and Thrace, led by their kings, Ostrogotha and Kniva.
Beginning in 253, the Crimean Goths and the Heruli appeared and dared to venture on the seas, ravaging the shores of the Black Sea and the Aegean as well as several Greek towns. In 267 Athens was taken and plundered despite a strong defense by the historian Dexippus. After the victories of Gallienus on the Nestus and Claudius at Naissus (Nish), there was for a time less danger. But the countries of the middle Danube were still under pressure by the Marcomanni, Quadi, Iazyges, Sarmatians, and the Carpi of free Dacia, who were later joined by the Roxolani and the Vandals. In spite of stubborn resistance, Dacia was gradually overwhelmed, and it was abandoned by the Roman troops, though not evacuated officially. When Valerian was captured in AD 259/260, the Pannonians were gravely threatened, and Regalianus, one of the usurpers proclaimed by the Pannonian legions, died fighting the invaders. The defense was concentrated around Sirmium and Siscia-Poetovio, the ancient fortresses that had been restored by Gallienus, and many cities were burned.
In the West the invasions were particularly violent. The Germans and the Gauls were driven back several times by the confederated Frankish tribes of the North Sea coast and by the Alemanni from the middle and upper Rhine. Gallienus fought bitterly, concentrating his defense around Mainz and Cologne, but the usurpations in Pannonia prevented him from obtaining any lasting results. In 259–260 the Alemanni came through the Agri Decumates (the territory around the Black Forest), which was now lost to the Romans. Some of the Alemanni headed for Italy across the Alpine passes; others attacked Gaul, devastating the entire eastern part of the country.
Passing through the Rhône Valley, they eventually reached the Mediterranean; and some bands even continued into Spain. There they joined the Franks, many of whom had come by ship from the North Sea, after having plundered the western part of Gaul. Sailing up the estuaries of the great rivers, they had reached Spain and then, crossing the Strait of Gibraltar, had proceeded to Mauretania Tingitana. Gallienus, outflanked, entrusted Gaul and his young son Saloninus to Postumus, who then killed Saloninus and proclaimed himself emperor.
The several invasions had so frightened the people that the new emperor was readily accepted, even in Spain and Britain. He devoted himself first to the defense of the country and was finally considered a legitimate emperor, having established himself as a rival to Gallienus, who had tried in vain to eliminate him but finally had to tolerate him. Postumus governed with moderation, and, in good Roman fashion, minted excellent coins. He, too, was killed by his soldiers, but he had successors who lasted until 274.
One reason for the fall of the Western Roman Empire was the expansion of the Goths. Unlike their present-day namesakes, these were a Scandinavian people from the Gothic lands of what is now southern Sweden, although the Gothic leadership and “high society” likely came from the island of Gotland, which lies in the Baltic Sea between Sweden and Latvia. Sometime around the years 100 BC to 100 CE, the northern Goths first moved to Poland, and after settling the area around Gdánsk for four-five generations, continued on along the Vistula and Danube rivers and then spread across modern Russia and Ukraine and occupied much of the land between the Baltic and the Black Sea, an area known as Reidgotaland or Aujum/Oium in historical sources, where they became known as the Ostrogoths.
It should be noted that, contrary to popular belief, the term Visigoth was not originally used to describe the Goths (and various indigenous steppe-nomadic cultures) that formed Reidgotaland aka the Kingdom of Aujum.
The Huns, a warring nomadic people attacking Reidgotaland from central Asia in the 270s CE, caused the Goths — who by now had split up into two major historical groups — the Ostrogoths and the Visigoths — to flee across the Danube river into the relative safety of the Roman Empire. Some Ostrogoths were left behind and had no choice but to join the Hunnic hordes, these Goths became the Gothunni, and are by all accounts known as “hraið-gutar” in Old Norse in Icelandic literary sources, which means “horse goths.”
