Archeologists dig up some cool stuff relevant to a battle between the Romans and a war like Germanic tribe, the Batavians.

From the always good History Blog.

Archaeologists excavating the North Rhine-Westphalian town of Krefeld have unearthed thousands of artifacts attesting to a 1st century rebellion of Batavian tribesemen against Rome. 

The Batavians, whose native territory was the delta between the Lower Rhine and the Waal, were long-time allies of Rome. Considered the bravest of all Germanic tribes, they had formed the core of the imperial guard since Augustus and had a special deal with the empire that exempted them from all tribute and taxes. The only resources the Batavians were required to contribute were fighting men, infantry and especially cavalry, famed for their amphibious ability to cross rivers on horseback in full armour.

Well regarded for their skills in horsemanship and swimming—for men and horses could cross the Rhine without losing formation, according to Tacitus. Dio Cassius describes this surprise tactic employed by Aulus Plautius against the "barbarians"—the British Celts— at the battle of the River Medway:

The barbarians thought that Romans would not be able to cross it without a bridge, and consequently bivouacked in rather careless fashion on the opposite bank; but he sent across a detachment of Germanic tribesmen, who were accustomed to swim easily in full armour across the most turbulent streams. [...] Thence the Britons retired to the river Thames at a point near where it empties into the ocean and at flood-tide forms a lake. This they easily crossed because they knew where the firm ground and the easy passages in this region were to be found; but the Romans in attempting to follow them were not so successful. However, the Germans swam across again and some others got over by a bridge a little way up-stream, after which they assailed the barbarians from several sides at once and cut down many of them. (Cassius Dio, Roman History, Book 60:20)

The Batavi were used to form the bulk of the Emperor's personal Germanic bodyguard from Augustus to Galba. They also provided a contingent for their indirect successors, the Emperor's horse guards, the Equites singulares Augusti.

A Batavian contingent was used in an amphibious assault on Ynys Mon (Anglesey), taking the assembled Druids by surprise, as they were only expecting Roman ships.

Numerous altars and tombstones of the cohorts of Batavi, dating to the 2nd century and 3rd century, have been found along Hadrian's Wall, notably at Castlecary and Carrawburgh, Germany, Yugoslavia, Hungary, Romania and Austria.

They contributed soldiers in far greater proportion than other Roman allies, an estimated 5,000 men out of a total population of just 35,000.

In 69 AD, the turbulent Year of the Four Emperors that followed the death of Nero, Rome pissed off the wrong Batavians. The year before Fonteius Capito, the governor of Germania Inferior had had Batavian prince Julius Paullus executed on false charges of rebellion. He sent Paullus’ kinsman Gaius Julius Civilis to Nero in chains on the same trumped up charges, but Nero died before rendering judgment. His successor Galba acquitted Civilis and sent him home. He also dissolved the Germanic bodyguard, however, and the Batavians saw this as a grave insult.

Then came the conscriptions. Roman chronicler Tacitus describes this trigger of the Batavian rebellion in his Histories in reliably salacious terms:

At the orders of Vitellius a levy of the young Batavians was now being made. This burden, which is naturally grievous, was made the heavier by the greed and licence of those in charge of the levy: they hunted out the old and the weak that they might get a price for letting them off; again they dragged away the children to satisfy their lust, choosing the handsomest — and the Batavian children are generally tall beyond their years. 

Civilis, who had already decided to rebel against at Rome, used this latest outrage as a fulcrum to move the whole tribe to rebellion and soon persuaded neighboring tribes to join in the cause.

Imagine if the arrogant Romans had simply had more self control.  Treat the allies, as least, as friends, not like that!  Who wouldn't rebel and seek the blood of such barbarians!

The Roman line was drawn up to oppose them not far from the Rhine, and the vessels which had been brought here after the burning of the forts were turned to front the foe. The battle had not lasted long when a cohort of the Tungri transferred its standards to Civilis, and the Roman soldiers, demoralized by this sudden betrayal, were cut down by allies and foes alike. There was the same treachery also on the part of the fleet: some of the rowers, being Batavians, by pretending a lack of skill interfered with the sailors and combatants; presently they began to row in the opposite direction and bring the sterns to the bank on which the enemy stood; finally, they killed such of the helmsmen and centurions as did not take their view, until the entire fleet of twenty-four vessels either went over to the enemy or was captured.

This victory was glorious for the enemy at the moment and useful for the future. They gained arms and boats which they needed, and were greatly extolled as liberators throughout the German and Gallic provinces.

Given the history of the region, it's surprising a larger rebellion in both Germany and Gaul didn't break out and send the Romans retreating back over the Alps.

Hubris, meet Nemesis.