The discoveries at Kalefeld (see previous posts here and here) have been attributed to the third century soldier emperor Maximinus Thrax. Little is known about him, and most of what the ancient sources write is probably wrong. The best summary is Michael Meckler's account at De Imperatoribus Romanis which also has a bibliography.
Only three ancient writers comment on his reign. Zosimus, writing much later, mentions him (1.13), but only in passing. The Historia Augusta devotes an entire book to him. Even though anything in the HA has to be treated with kid gloves, I do, however, like the description of his eating habits (Maximini Duo, 4):
The physical description of him (Maximini Duo, 6) is also entertaining:
More seriously, there is a version of Maximinus' campaign in Germany (Maximini Duo, 11-12), but the account clearly derives from Herodian. It is his account of Maximinus' Germanic wars (Herodian 7, 1-2) that has been jumped on by commentators at Kalefeld. Here is his version in full:
Maximinus was aroused to even greater fury by a plot allegedly formed by many centurions and all the senators. A man of the nobility and consular rank named Magnus was accused of organising a conspiracy against the emperor and persuading some of the soldiers to transfer the empire to his charge. The plot was said to be something like this. Maximinus had bridged the Rhine River and was about to cross over and attack the Germans; for, as soon as he got control of the empire, he immediately began military operations. Since it appeared that he had been chosen emperor because of his great size, military prowess, and experience in war, he undertook to confirm by action the good reputation and high esteem he enjoyed among the soldiers. In this way, too, he tried to demonstrate that the charges of vacillation and timidity in military matters they brought against Alexander were well founded. Therefore he did not halt the soldiers' training and exercises, and remained under arms himself, spurring the army to action.
There follows a discussion of a plot to betray Maximinus to the Germans.
Having settled affairs in the manner described above, Maximinus led out his entire army and crossed the bridge fearlessly, eager to do battle with the Germans. Under his command was a vast number of men, virtually the entire Roman military force, together with many Moroccan javelin men and Osroenian and Armenian archers; some were subject peoples, others friends and allies, and included, too, were a number of Parthian mercenaries and slaves captured by the Romans.
This enormous force was originally assembled by Alexander, but it was increased in size and trained for service by Maximinus. The javelin men and archers seemed to be especially effective against the Germans, taking them by surprise, attacking with agility and then retreating without difficulty.
Though he was in enemy territory, Maximinus advanced for a considerable distance because all the barbarians had fled and he met no opposition. He therefore laid waste the whole country, taking particular care to destroy the ripening grain, and burned the villages after allowing the army to plunder them. Fire destroys the German towns and houses very quickly.
Although there is a scarcity of stone and fired brick in Germany, the forests are dense, and timber is so abundant that they build their houses of wood, fitting and joining the squared beams. Maximinus advanced deep into German territory, carrying off booty and turning over to the army all the herds they encountered.
The Germans had left the plains and treeless areas and were hiding in the forests; they remained in the woods and marshes so that the battle would have to take place where the thick screen of trees made the missiles and javelins of their enemies ineffectual and where the depths of the marshes were dangerous to the Romans because of their unfamiliarity with the region. The Germans, on the contrary, were well acquainted with the terrain and knew which places provided firm footing and which were impassable. They moved rapidly and easily through the marshes, in water only knee-deep.
The Germans, who do all their bathing in the rivers, are expert swimmers. As a result, most of the skirmishing occurred in those regions, and it was there that the emperor personally and very boldly joined battle. When the Germans rushed into a vast swamp in an effort to escape and the Romans hesitated to leap in after them in pursuit, Maximinus plunged into the marsh, though the water was deeper than his horse's belly; there he cut down the barbarians who opposed him.
Then the rest of the army, ashamed to betray their emperor who was doing their fighting for them, took courage and leaped into the marsh behind him. A large number of men fell on both sides, but, while many Romans were killed, virtually the entire barbarian force was annihilated, and the emperor was the foremost man on the field. The swamp pool was choked with bodies, and the marsh ran red with blood; this land battle had all the appearance of a naval encounter.
This engagement and his own bravery Maximinus reported in dispatches to the senate and Roman people; moreover, he ordered the scene to be painted on huge canvases to be set up in front of the senate house, so that the Romans might not only hear about the battle but also be able to see what happened there. Later the senate removed this picture together with the rest of his emblems of honour. Other battles took place in which Maximinus won praise for his personal participation, for fighting with his own hands, and for being in every conflict the best man on the field.
After taking many German prisoners and seizing much booty, the emperor, since winter had already begun, went to Pannonia and spent his time at Sirmium, the largest city in that country; there he made preparations for his spring offensive. He threatened (and was determined) to defeat and subjugate the German nations as far as the ocean.