Marcus Hordeonius Flaccus (c.14-69): Roman senator, commander of the Rhine army during the Batavian revolt. His reputation has suffered severely from the biased description of his campaigns in the Rhineland by the Roman historian Tacitus.
Although the political situation was unclear, Marcus Hordeonius Flaccus sent the two (half) legions that were stationed at Xanten to the Island of the Batavians (V Alaudae and XV Primigenia). But they were defeated in the neighborhood of Nijmegen and forced to return to their base. This was a very serious matter. Even worse, there were eight well-trained Batavian auxiliary units that no longer obeyed the orders of the emperor Vitellius, and had decided to go back home. It was not clear whether they wanted to join the rebels, or were merely tired of the endless fighting (they had constantly been active for more than 18 months).
Flaccus happened to be at Mainz, where the remains of the legions IIII Macedonica and XXII Primigenia were garrisoned, at the moment when the eight units arrived from the south.
He called his tribunes and centurions together and consulted them on the desirability of bringing the insubordinate troops to heel by force. But he was not by nature a man of action, and his staff were worried by the ambiguous attitude of the auxiliaries and the dilution of the legions by hasty conscription. So he decided against risking his troops outside the camp. Afterwards, he changed his mind, and as his advisers themselves went back on the views they had expressed, he gave the impression that he intended pursuit, and wrote Herennius Gallus, stationed at Bonn in command of the First legion, telling him to bar the passage of the Batavians and promising to follow closely in their heels with his army. The rebels could in fact have been crushed if Hordeonius Flaccus and Herennius Gallus had moved from opposite directions and caught them between two fires. But Flaccus abandoned his plan, and in a fresh dispatch to Gallus warned him not to molest the departing units.note[Tacitus, Histories 4.19; tr. Kenneth Wellesley.]
It is unclear what really happened. Tacitus obviously blames Flaccus for not destroying the eight units, but things were more complicated than he indicates. We must remember that Germania Inferior, which was threatened by the Batavians, was not an important province; Germania Superior and Gallia Belgica, however, were. Probably, Flaccus wanted to leave the problem in the periphery, and allowed the Batavians to return home. Then, the war would remain somewhere in the north, where it did not threaten vital Roman interests. Localizing the war where it did not really hurt could have been a successful strategy, but eventually, Flaccus was murdered, after which everything went wrong.
A second point is that both Roman armies in Mainz and Bonn were smaller than the eight auxiliary units. Only when Flaccus and Gallus were able to attack simultaneously, they were in the majority and could be victorious. Flaccus could not afford that both armies were defeated. Finally, there was a more important war going on in Italy, and he could not move too far to the north. So he decided upon this strategy: keep the vital base of Mainz at all costs, try to keep Xanten, and wait until the civil war is over.
However, there was some risk involved: the Batavians would be stronger. And indeed, they laid siege to Xanten (late September). However, Flaccus had already sent reinforcements to the the legionary base. Tacitus does not say this explicitly, but he does mention the presence of the commander of the Sixteenth legion Gallica, which shows that troops from Neuss had been directed to Xanten.
Before the siege started, Julius Civilis had made his men swear allegiance to Vespasian, and sent an appeal to the legionaries he was about to besiege, asking them to accept the same oath. This was a clever move, because, as we have already seen above, Flaccus would be handicapped: if Vespasian were victorious and the Rhine army had defeated his allies, this could be explained as an attempt to obstruct the accession of the new emperor. The legions of Germania Superior had experience with this phenomenon: after all, the only result of their victory over Gaius Julius Vindex had been that Galba mistrusted them.
So, Flaccus had to be careful, especially since the army of the Danube had sided with Vespasian and was marching to Italy. Nevertheless, the commander of the Rhine army decided not to take any risks, and organized a rescue force.
Pickets were posted along the Rhine to prevent the Germans from entering the empire. He ordered the Fourth legion Macedonica to stay at Mainz, which had to be kept at all costs. Messengers were sent to Gaul, Hispania, and Britain, requesting for reinforcements. (As we will see, Basque units were to save the day during a battle near Krefeld.) The Twenty-second legion Primigenia, commanded by Gaius Dillius Vocula, marched at top speed to Neuss; Flaccus himself went to the First legion Germanica at Bonn, traveling on board a naval squadron because he suffered from gout.
At Bonn, something went wrong: the legionaries of the first legion refused to obey orders from Flaccus. However, he had one of the mutineers arrested, and proceeded to Cologne.
Among the legions there was growing resentment, and they had not bee intimidated by the confinement of one solitary soldier. Indeed, the fellow actually tried to incriminate the governor [Flaccus], alleging that he had himself carried messages between Julius Civilis and Flaccus, and was being got rid of on a trumped-up charge because he knew too much. Vocula showed remarkable firmness. He got up on a platform and ordered the man to be seized and taken away, still yelling, to execution. This gave the trouble-makers a shock, and the better sort obeyed orders. Then, as they called unanimously for Vocula to lead them, Flaccus handed over the command to him.note[Tacitus, Histories 4.26; tr. Kenneth Wellesley.]
The real reason why the old Flaccus handed over the command of the advance guard (which is not the same as the command of the whole army), probably was his gout. Besides, a Roman general had other occupations than his military responsibilities. Vespasian's army was on its way to Italy, and the political situation at home demanded Flaccus' attention. He stayed at Neuss, and Vocula led the advance guard to Krefeld.
Here, the Roman advance halted. Tacitus offers all kinds of reasons for the delay: the soldiers had to receive extra training, the Cugerni (a tribe inside the empire that had sided with Civilis) had to be punished, they had to fight with enemies for the possession of a heavily-laden corn-ship... The real reason was that, for the time being, it was unwise to behave too aggressive against people who called themselves adherents of Vespasian.
In the first days of November, the soldiers received bad news: their emperor Vitellius and his army -which was made up from units from the Rhine- had been defeated. Those at Krefeld personally knew many of the dead. This did little to improve the morale, especially since it was clear that Vitellius could no longer win the civil war. There was no other solution than to go over to Vespasian's side.
When Hordeonius Flaccus administered the oath of allegiance, the rank-and-file accepted it under pressure from the officers, though with little conviction in their looks or hearts, and while firmly reciting the other formulae of the solemn declaration, hesitated at the name "Vespasian" or mumbled it, and indeed for the most passed it over in silence.note[Tacitus, Histories 4.31; tr. Kenneth Wellesley.]
Again, Flaccus was forced to wait. He did not know what to do, Julius Civilis had to take the initiative. If the Batavian leader had truly been an adherent of Vespasian, the war was now over, because the legions of the Rhine army had sided with this emperor. If, on the other hand, his use of the letter from Vespasian had been nothing but a masquerade, the war had to continue, and the Romans would have to fight with the bravest of all neighboring tribes. Slowly, the days passed on, and nothing happened. No messengers arrived from the north, and Flaccus understood that the Batavian wanted to continue the struggle.
Civilis knew that he had to destroy the army at Krefeld before it had united with the besieged. If he had defeated the expeditionary force of Flaccus and Vocula, Xanten could no longer be relieved and would surrender. However, the army of Flaccus and Vocula, even though it consisted of depleted legions, was too large to face in a regular battle. Flaccus and Vocula understood that the Batavian leader would try to catch them off-guard. And they could also surmise that he would do this on a moonless night, like the night of December 1/2, 69. Tacitus, however, wants us to believe that the Batavian attack on Krefeld came unexpectedly.
Vocula was unable to address his men or deploy them in line of battle. All he could do when the alarm sounded was to urge them to form a central core of legionaries, around which the auxiliaries were clustered in a ragged array. The cavalry charged, but were brought up short by the disciplined ranks of the enemy and forced back upon their fellows. What followed was a massacre, not a battle. The Nervian auxiliary units, too, were induced by panic or treachery to expose the Roman flanks. Thus the attack penetrated to the legions. They lost their standards, retreated within the rampart, and were already suffering heavy losses there, when fresh help suddenly altered the luck of the battle.
Some Basque auxiliary units [...] had been summoned to the Rhineland. As they neared the camp, they heard the shouts of men fighting. While the enemy's attention was elsewhere, they charged them from the rear and caused a widespread panic out of proportion to their numbers. It was thought that the main army had arrived, either from Neuss or from Mainz. This misconception gave the Romans new heart: confident in their strength of others, they regained their own.note[Tacitus, Histories 4.33; tr. Kenneth Wellesley.]
Again, Tacitus' description is misleading to the extreme. Of course the Basque units did not arrive by accident, as Tacitus seems to imply. It must have been sent by Flaccus, who was at Neuss.
The consequences of the Roman victory were enormous. Civilis had shown his true intentions and lost his best men, and nothing withheld Vocula from marching on Xanten and lifting the siege. (Flaccus remained at Neuss.) However, when Vocula's legions were preparing the invasion of the Island of the Batavians, bad news arrived from the south: the Usipetes and Chattians, Germanic tribes from the east bank of the Rhine, had crossed the river, were plundering the country and tried to besiege Mainz. It did not seem very serious, but Flaccus did not want to take any risks. Therefore, he recalled Vocula's army. After all, Mainz was more important than the camp in the north.
When the legionaries reached Neuss, there was a pleasant surprise: Flaccus distributed money to celebrate the accession of Vespasian. As loyal adherents of Vitellius, this was more than they had expected. December 17 was the day of the Roman carnival, the Saturnalia, and the legionaries celebrated it with pleasure. It must have come as some sort of release after the tensions of the preceding weeks. However, the merrymaking was disturbed.
In a wild riot of pleasure, feasting and seditious gatherings at night, their old enmity for Hordeonius Flaccus revived, and as none of the officers dared to resist a movement which darkness had robbed of its last vestige of restraint, the troops dragged him out of bed and murdered him. The same fate was in store for Vocula, but he disguised himself in the darkness by dressing as a slave, and managed to get away.note[Tacitus, Histories 4.36; tr. Kenneth Wellesley.]
The assault on the two commanders at the moment when Fortune was smiling at the Romans, is one of the unexplained events during the Batavian revolt. (Go here for a possible explanation.) It was certainly not an act that all soldiers approved of, because Vocula could return to the camp and restore order. Then, he continued to the south and relieved Mainz.
However, the murder of Flaccus by his own men, just after he had restored order at Bonn, Cologne, Neuss, and Xanten, gave the defeated rebels new self-confidence. Julius Civilis renewed the siege of Xanten, and the Trevirans and Lingones, ancient Gallic but romanized tribes living along the Mosel and upper Rhine, decided to revolt, too. This was more than Vocula and the remaining legionaries could handle. In January 70, Vocula was killed, and his army surrendered to the rebels. Two months later, the garrison of Xanten was massacred.
Only Mainz remained. Marcus Hordeonius Flaccus had decided that the first objective was to keep this legionary base, and this strategy was successful. When Quintus Petillius Cerialis arrived in the summer of 70 with a large expeditionary force, he could rely on this stronghold, which made it a lot easier to suppress the rebellion.
Flaccus' year as governor of the Germanic provinces had been a catastrophe, but he had rescued what could be rescued: Mainz. This was certainly not without merit, but the new emperor could not admit this. His own role had been very dubious - in fact, it was high treason - so he needed someone who could be blamed. Flaccus' reputation was forever blackened.