For the next five years, the Huns stayed out of Roman sight as they tried to invade the Persian Empire. A crushing defeat in Armenia caused them to abandon this attempt and return their attentions to Europe. In 440, they reappeared on the borders of the Roman Empire, attacking the merchants at the market on the north bank of the Danube that had been established by the treaty. Attila and Bleda threatened further war, claiming that the Romans had failed to fulfill their treaty obligations and that the Bishop of Margus had crossed the Danube to ransack and desecrate the royal Hun graves on the Danube's north bank. They crossed the Danube and laid waste to Illyrian cities and forts on the river, among them, according to Priscus, Viminacium (present-day Kostolac), which was a city of the Moesians in Illyria. Their advance began at Margus, for when the Romans discussed handing over the offending bishop, he slipped away secretly to the Huns and betrayed the city to them.