But for unknown reasons, this was not enough for the Batavians. Civilis chose to pursue vengeance and swore to destroy the two Roman legions. The timing was well chosen. With the civil war of the Year of the Four Emperors at its peak, it would take some time before Rome could produce an effective counterattack. Moreover, the eight Batavian auxiliary units of Vitellius' army were on their way home and could be easily persuaded to join the rebellion for an independent Batavia. This was an important reinforcement. Apart from being veteran troops, their numbers were greater than the combined Roman troops stationed in Moguntiacum (Mainz) and Bonna (Bonn).