In AD 6, Tiberius was about to launch the second campaign against the Marcomanni in Germania. Marcus Valerius Messalla Messallinus, the governor of Illyricum, had planned to join him with most of his army, and ordered the local tribes to provide auxiliary contingents. However, when these troops gathered, they rebelled under the leadership of a Daesitiate tribal chieftain named Bato and defeated a Roman force sent against them. Although this war is sometimes described as having been fought by the Daesitiatae and the Breuci only, Cassius Dio identified the forces led by Bato the Daesitiate as Dalmatian, indicating a broader composition. According to Velleius Paterculus, the population of the tribes which rebelled was more than 800,000, and they fielded 200,000 infantry and 9,000 cavalry. Modern scholars cannot be certain of how trustworthy this information is, as ancient historians tended to exaggerate figures. Velleius Paterculus also wrote that the rebels knew Roman military tactics and spoke Latin.