Sclaveni are first mentioned in the context of the military policy on the Danube frontier of Byzantine Emperor Justinian I (r. 527–565). In 537, 1,600 cavalry, made up of mostly Sclaveni and Antes, were shipped by Justinian to Italy to rescue Belisarius. Sometime between 533–34 and 545 (probably before the 539–40 Hun invasion), there was a conflict between the Antes and Sclaveni in Eastern Europe. Procopius noted that the two "became hostile to one another and engaged in battle" until a Sclavene victory. The conflict was likely aided or initiated by the Byzantines. In the same period, the Antes raided Thrace. The Romans also recruited mounted mercenaries from both tribes against the Ostrogoths. The two tribes were at peace by 545. Notably, one of the captured Antes claimed to be Roman general Chilbudius (who was killed in 534 by barbarians at the Danube). He was sold to the Antes and freed. He revealed his true identity but was pressured and continued to claim that he was Chilbudius. The Antes are last mentioned as anti-Byzantine belligerents in 545, and the Sclaveni continued to raid the Balkans. The Antes became Roman allies by treaty in 545. Between 545 and 549, the Sclaveni raided deep into Roman territory. In 547, 300 Antes fought the Ostrogoths in Lucania. In the summer of 550, the Sclaveni came close to Naissus, and were seen as a great threat, however, their intent on capturing Thessaloniki and the surroundings was thwarted by Germanus. After this, for a year, the Sclaveni spent their time in Dalmatia "as if in their own land". The Sclaveni then raided Illyricum and returned home with booty. In 558 the Avars arrived at the Black Sea steppe, and defeated the Antes between the Dnieper and Dniester. The Avars subsequently allied themselves with the Sclaveni.