Vitellius had become emperor and needed soldiers to defend himself against general Vespasian, who was marching on Rome from Judaea. Eight Batavian auxiliary infantry units were on their way to Italy, but the emperor still needed more men. Therefore, he ordered the commander of the Rhine army, Marcus Hordeonius Flaccus, to sent extra troops.
Our main source for the events in the years 69 and 70, the Histories of the Roman historian Tacitus (c.55-c.120), does not have got a good word to say about general Flaccus. Tacitus thinks he was indolent, insecure, slow, and responsible for the Roman defeats in 69. However, in his description of the Batavian revolt, he constantly opposes the civilized but decadent Romans and the savage but noble Batavians (a trick he also employs in his Origins and customs of the Germans). His idealized portrait of the leader of the Batavians, Julius Civilis, is mirrored in the portrayal of Flaccus as an incompetent defeatist. They are extreme types.
Of course it is possible that Flaccus was really incompetent, but if we ignore Tacitus' personal judgments and carefully look at what the commander of the Rhine army actually did, there is no reason to doubt that he was a capable commander who did what he could in a very, very difficult situation.The least one can say for Flaccus, is that he recognized the approaching troubles: he refused to support Vitellius, seeing that it was ill-advised to remove more soldiers from the border.
After Flaccus' refusal, Vitellius demanded that new soldiers would be recruited. This measure was meant as a deterrent to future rebels and might have worked well, but no Batavian was impressed by the measure, as there were no troops in the neighborhood to implement the treath. Tacitus writes:
Batavians of military age were being conscripted. The levy was by its nature a heavy burden, but it was rendered still more oppressive by the greed and profligacy of the recruiting sergeants, who called up the old and unfit in order to exact a bribe for their release, while young, good-looking lads (for children are normally quite tall among the Batavians) were dragged off to gratify their lust. This caused bitter resentment, and the ringleaders of the prearranged revolt succeeded in getting their countrymen to refuse service.
The Batavians lived along the great rivers in the Netherlands on a large island between the rivers Waal and Rhine. (Their name lives on the present name of the island, Betuwe.)
The Island was a relatively poor country, which could not be exploited financially by the Romans. Therefore, the Batavians contributed only men and arms to the empire: eight auxiliary units of infantry, one squadron of cavalry, and -until the Galba dismissed them- the mounted bodyguard of the emperor. Demographic research has led to the conclusion that every Batavian family had at least one son in the army. Recruiting more men was almost impossible, and it comes as not surprise to find the sergeants calling up the old, the unfit, and the young. Tacitus continues his story.
Julius Civilis invited the nobles and the most enterprising commoners to a sacred grove, ostensibly for a banquet. When he saw that darkness and merriment had inflamed their hearts, he addressed them. Starting with a reference to the glory and renown of their nation, he went on to catalogue the wrongs, the depredations and all the other woes of slavery. The alliance, he said, was no longer observed on the old terms: they were treated as chattels.