The German historician Alexander Demandt enumerates in his fascinating book Der Fall Roms (“The Fall of Rome”, 1984) no less than 210 factors that contributed to the collapse of the Roman Empire, arranged alphabetically from Aberglaube, “idolatry”, to Zweifrontenkrieg, “war on two fronts”. This illustrates a debate about the causes of the demise of the ancient world that has now lasted more than two, three centuries. It is unlikely that we will ever reach consensus.
All modern authors agree on one point, however: when the Vandals, Suebians, and Alans invaded the empire on the last day of 406, an event that must have played a role in the transformation from Antiquity to Middle Ages, they crossed a river Rhine that was frozen.
But how do we know? The subject has been debated at RomanArmyTalk, where it was shown that this little detail was not in our sources, and that it was probably invented by the British ancient historian Edward Gibbon (1737-1794). In 1781, he wrote in chapter 30 of his famous History of the Decline and Fall of the Roman Empire:
‘On the last day of the year, in a season when the waters of the Rhine were most probably frozen, they entered without opposition the defenceless provinces of Gaul.’
Why did he speculate that the river must have been frozen? Partly to explain why the barbarians didn’t meet any opposition, we’re tempted to think – and probably, we’re right. However, it may also be relevant that Gibbon used to live in Switzerland for some time, and may have seen how the upper reaches of the Rhine can indeed be covered by ice. And he certainly read the following lines by Herodian, who presents an account of extreme circumstances as if it is a description of an average winter. Gibbon, who had never seen the Middle and Lower Rhine, may well have been led astray by his excellent command of the sources – in this case, Herodian, Roman History, 6.7.6-8:
The Rhine in Germany and the Danube in Pannonia are the largest of the northern rivers. In summer their depth and width make them easily navigable, but in the cold winters they freeze over and appear like a level plain which can be crossed on horseback.The river becomes so firm and solid in that season that it supports horses and men. Then those who want drinking water do not come to the river with pitchers and bowls; they bring axes and mattocks and, when they have finished chopping, take up water without using bowls and carry it in chunks as hard as rock. Such is the nature of these rivers