The Rain Miracle: the miraculous escape of the Twelfth Legion Fulminata during the Marcomannic Wars.
Immediately, there were several traditions about the cause of the miracle. According to Cassius Dio, a Greek historian who wrote some 40 years after the event, an Egyptian magician had been able to work the miracle (Roman History, 72=71.8-10). On the other hand, his contemporary Tertullian, a Christian author, claimed that the prayer of Christian soldiers had caused the miracle. Other sources on the incident are coins and a relief on the honorary column of Marcus Aurelius.
The Roman History of Cassius Dio is partly lost, but an excerpt by the Byzantine author Xiphilinus survives. It is quoted below, including an addition by Xiphilinus, who accuses Dio of fraud.
The translation was made by E. Cary.
[71.8] So Marcus subdued the Marcomanni and the Iazyges after many hard struggles and dangers. A great war against the people called the Quadi also fell to his lot and it was his good fortune to win an unexpected victory, or rather it was vouchsafed him by heaven.For when the Romans were in peril in the course of the battle, the divine power saved them in a most unexpected manner. The Quadi had surrounded them at a spot favorable for their purpose and the Romans were fighting valiantly with their shields locked together; then the barbarians ceased fighting, expecting to capture them easily as the result of the heat and their thirst. So they posted guards all about and hemmed them in to prevent their getting water anywhere; for the barbarians were far superior in numbers. The Romans, accordingly, were in a terrible plight from fatigue, wounds, the heat of the sun, and thirst, and so could neither fight nor retreat, but were standing and the line and at their several posts, scorched by the heat, when suddenly many clouds gathered and a mighty rain, not without divine interposition, burst upon them. Indeed, there is a story to the effect that Harnuphis, an Egyptian magician, who was a companion of Marcus, had invoked by means of enchantments various deities and in particular Mercury, the god of the air,note[Mercury is not known as celestial deity. He is, however, often presented as the Roman equal of the Egyptian Thoth, who is, under the name of Thoth-Shu, responsible for meteorology.] and by this means attracted the rain.
[71.9]This is what Dio says about the matter, but he is apparently in error, whether intentionally or otherwise; and yet I am inclined to believe his error was chiefly intentional. It surely must be so, for he was not ignorant of the division of soldiers that bore the special name of the "Thundering" legion - indeed he mentions it in the list along with the others- a title which was given it for no other reason (for no other is reported) than because of the incident that occurred in this very war.note[The honorary title Fulminata ("thundering" or "lightning") was in fact used more than a century before the rain miracle. Xiphilinus' diatribe against Dio misses all foundation.] It was precisely this incident that saved the Romans on this occasion and brought destruction upon the barbarians, and not Harnuphis, the magician; for Marcus is not reported to have taken pleasure in the company of magicians or in witchcraft.note[This is far from certain. Marcus Aurelius had a great reputation as a philosopher, but in the late second century, wisdom involved non-rational approaches of the divine. Harnuphis is known from n inscription that was found at Aquileia, one of Marcus Aurelius' military bases.] Now the incident I have reference to is this: Marcus had a division of soldiers (the Romans call a division a legion) from Melitene; and these people are all worshippers of Christ. Now it is stated that in this battle, when Marcus found himself at a loss what to do in the circumstances and feared for his whole army, the prefect approached him and told him that those who are called Christians can accomplish anything whatever by their prayers and that in the army there chanced to a whole division of this sect. Marcus on hearing this appealed to them to pray to their God; and when they had prayed, their God immediately gave ear and smote the enemy with a thunderbolt and comforted the Romans with a shower of rain. Marcus was greatly astonished at this and not only honored the Christians by an official decree but also named the legion the 'thundering' legion. It is also reported that there is a letter of Marcus extant on the subject. But the Greeks, though they know that the division was called the "thundering" legion and themselves bear witness to the fact, nevertheless make no statement whatever about the reason for its name.
[71.10]Dio goes on to say that when the rain poured down, at first all turned their faces upwards and received the water in their mouths; then some held out their shields and some their helmets to catch it, and they not only took deep draughts themselves but also gave their horses to drink. And when the barbarians now charged upon them, they drank and fought at the same time; and some, becoming wounded, actually gulped down the blood that flowed into their helmets, along with the water. So intent, indeed, were most of them on drinking that they would have suffered severely from the enemy's onset, had not a violent hail-storm and numerous thunderbolts fallen upon the ranks of the foe. Thus in one and the same place one might have beheld water and fire descending from the sky simultaneously; so that while those on the one side were being consumed by fire and dying; and while the fire, on the one hand, did not touch the Romans, but, if it fell anywhere among them, was immediately extinguished, the shower, on the other hand, did the barbarians no good, but, like so much oil, actually fed the flames that were consuming them, and they had to search for water even while being drenched with rain. Some wounded themselves in order to quench the fire with their blood, and others rushed over to the side of the Romans, convinced that they alone had the saving water; in any case Marcus took pity on them. He was now saluted Imperator by the soldiers, for the seventh time; and although he was not wont to accept any such honor before the Senate voted it, nevertheless this time he took it as a gift from heaven, and he sent a dispatch to the senate.