To the 432 , the Huns were united under King Rua or Rugila. At 434 Rua died, leaving his nephews Attila and Bledsoe , Mundzuk sons of his brother, commanding all the Hun tribes. At that time the Huns were in the middle of negotiations with the ambassadors of Theodosius II about the delivery of several renegade tribes who had taken refuge within the Eastern Empire . The following year, Attila and Bledsoe had a meeting with the imperial legation at Margus (present Pozarevac ) and, when sitting on the rump of the horses to the huna way, negotiated a treaty. The Romans agreed not only to return the fugitive tribes (who had been a most welcome aid against the Vandals ), but also double the tax previously paid by the empire, Roman 350 pounds of gold (about 115 kg), open markets Huns and traders pay a ransom of eight solid for each Roman taken prisoner by the Huns. Here, satisfied with the treaty up their camps and headed inland, perhaps in order to consolidate and strengthen their empire. Theodosius used this opportunity to strengthen the walls of Constantinople , building the first sea walls of the city, and lift lines on the border defenses along the Danube.
The Huns remained out of sight of the Romans over the next five years. During this time carried out an invasion of Persia . However, a counter Persian Armenia ended with the defeat of Attila and Bledsoe, who gave up their plans of conquest. In the 440 reappeared on the borders of the Eastern Empire, attacking the merchants of the north bank of the Danube, which protected the existing treaty. Bledsoe Attila and threatened to open war, arguing that the Romans had failed to meet their commitments and that the bishop of Margus (near present Belgrade ) had crossed the Danube to ransack and desecrate the royal Hun graves on the north bank of the Danube. Then crossed the river and overran the Illyrian cities and forts along the shore, among them, according Prisco - Viminacium, which was a city of Moesia in Illyria. Their advance began at Margus, for when the Romans discussed the possibility of giving the bishop accused of desecration, he fled secretly to the barbarians and gave them the city.
Theodosius had unguarded coastal defenses as a result of the conquest of Carthage by the Vandals Genserico in 440 and the invasion of Armenia by the Sassanid Yazdegerd II in 441 . This left Bledsoe Attila and the open road through Illyria and the Balkans, who rushed to invade on the same 441 . The Hun army, having sacked Margus and Viminacium took Sigindunum (modern Belgrade ) and Sirmium before halting operations. There followed a truce along the 442 , Theodosius took time to bring its troops from North Africa and have a great printing money to finance the war against the Huns. Having made these preparations, felt he could afford to refuse the demands of the barbarian kings.
Attila's response was to resume the campaign Bleda ( 443 ). Pounding along the Danube, took the military establishments of Ratia and successfully besieged Naissus (current NIS ) through the use of battering rams and rolling towers assault (military sophistication novel between the Huns). Later, pressing along the Nisava occupied Serdica ( Sofia ), Philippopolis ( Plovdiv ) and Arcadiopolis . And destroyed by Roman troops clashed on the outskirts of Constantinople and was only halted by the lack of adequate material siege able to open gaps in the Cyclopean walls of the city. Theodosius admitted defeat and sent the courtier Anatolio to negotiate peace terms that were more stringent than in the previous treaty: the Emperor agreed to hand over 6,000 Roman pound (about 1,963 kg) of gold as compensation for missing the terms of the covenant, the yearly tribute was tripled, reaching the amount of 2,100 Roman pound (about 687 kg) of gold, and the ransom for each Roman prisoner happened to be 12 strong.
Satisfied their desires for a time, the Hun kings withdrew into his empire. According to Jordanes (who continues to Priscus ), sometime in the lull that followed the withdrawal of the Huns from Byzantium (probably around 445 ), Bleda died and Attila became the sole king. There is plenty of historical speculation about whether Attila murdered his brother or whether Bleda died from other causes. In any case, Attila was now the undisputed ruler of the Huns and again turned to the Eastern Empire.