In Cassius Dio's version, at first, Bato the Daesitiate had very few followers. However, once he defeated the Roman force sent against him, more rebels joined him. Then the Breuci, the largest tribe in southern Pannonia, led by a commander also named Bato, marched on Sirmium. Aulus Caecina Severus, the governor of the neighbouring province of Moesia (in modern Serbia, south of the River Sava and west of the River Danube) quickly advanced against them and defeated them near the River Dravus (Drava), but suffered many casualties. Hoping to renew the struggle soon because many Romans had fallen, the Breuci called on their allies to join them. Cassius Dio did not specify whether Severus broke a siege of the city or prevented the enemy from reaching it. The Drava was to the northwest of Sirmium and the Romans from Moesia must have come from the east or the south. Thus, if Caecina Severus did break a siege of Sirmium, he would have pursued the retreating Breuci until they made a last stand. The Dalmatians marched on Salona (in Dalmatia, on the Adriatic coast) but there Bato was defeated and wounded. He sent other men forward who ravaged the coast down to Apollonia. They were defeated in one battle, but won another. Tiberius came from Germania, fearing an invasion of Italy, and sent Valerius Messallinus ahead. Even though Bato was not well, he engaged Tiberius. Tiberius was stronger in open battle, but he was defeated in an ambush. Velleius Paterculus wrote that Messallinus was surrounded by 20,000 men and had only one legion at only half its normal strength (roughly 2,500 men), yet he routed the enemy and was awarded a triumph. Presumably Valerius Messallinus was then sent to defend Salona.