The legions Fifth legion Alaudae and Fifteenth legion Primigenia were besieged in Vetera. Marcus Hordeonius Flaccus, less indolent than Tacitus wants us to believe, had already taken counter-measures. 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, Spain, 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 Caius Dillius Vocula, marched at top speed to Novaesium or Neuss in the north; Flaccus himself went to the First legion Germanica at Bonn, traveling on board a naval squadron because he suffered from gout.
Tacitus tells us that at Bonn, the general found it difficult to take authoritative action. The soldiers held him responsible for the free passage of the eight Batavian auxiliary units. However, he convinced the First legion to follow him, and together with Vocula's legion, he joined forces with the Sixteenth legion Gallica at Neuss. They continued to Gelduba, modern Krefeld.
And then, suddenly, the advance halted. Tacitus offers all kinds of reasons for the delay: the soldiers had to receive additional training, the Cugernians (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, however, was that news had arrived from the south: the Roman army of the Danube had sided with Vespasian and invaded Italy.
It may be remembered that the army of the Rhine had fought for Nero against Caius Julius Vindex in 68 (above); nonetheless, Vindex' friend Galba had become emperor, and he had been suspicious of the Rhine army. Flaccus and Vocula, who was now serving as his right-hand man, wanted to prevent that this history would repeat itself. Suppose that they defeated Civilis, who claimed to fight for Vespasian, and suppose that the army of the Danube defeated Vitellius... This was an unacceptable risk.
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. The officers decided that they had to side with Vespasian.
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.
Again, Flaccus and Vocula were forced to wait. They did not know what to do, Julius Civilis had to take the initiative. If he 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. He knew that, after the attack on Vetera, the Romans would retaliate, but it would cost half a year before they could sent an army across the Alps -the winter was approaching- and if he had destroyed the army at Krefeld, he could take Vetera and enlarge the rebellious region. He was already negotiating with the Trevirans, who would certainly side with him if the most northerly position of the Roman forces were Mainz. However, Civilis was confronted with with one problem: the army of Flaccus and Vocula, even though it consisted of three depleted legions, was too large to face in a regular battle.