Campaigns against the Eastern Roman Empire
The death of Rugila (also known as Rua or Ruga) in 434 left the sons of his brother Mundzuk, Attila and Bleda, in control of the united Hun tribes. At the time of the two brothers' accession, the Hun tribes were bargaining with Eastern Roman Emperor Theodosius II's envoys for the return of several renegades who had taken refuge within the Eastern Roman Empire, possibly Hunnic nobles who disagreed with the brothers' assumption of leadership.
The following year, Attila and Bleda met with the imperial legation at Margus (Požarevac), all seated on horseback in the Hunnic manner, and negotiated an advantageous treaty. The Romans agreed to return the fugitives, to double their previous tribute of 350 Roman pounds (c. 115 kg) of gold, to open their markets to Hunnish traders, and to pay a ransom of eight solidi for each Roman taken prisoner by the Huns. The Huns, satisfied with the treaty, decamped from the Roman Empire and returned to their home in the Great Hungarian Plain, perhaps to consolidate and strengthen their empire. Theodosius used this opportunity to strengthen the walls of Constantinople, building the city's first sea wall, and to build up his border defenses along the Danube.
The Huns remained out of Roman sight for the next few years while they invaded the Sassanid Empire. They were defeated in Armenia by the Sassanids, abandoned their invasion, and turned their attentions back to Europe. In 440, they reappeared in force 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 of 435.
Crossing the Danube, they laid waste to the cities of Illyricum and forts on the river, including (according to Priscus) Viminacium, a city of Moesia. Their advance began at Margus, where they demanded that the Romans turn over a bishop who had retained property that Attila regarded as his. While the Romans discussed the bishop's fate, he slipped away secretly to the Huns and betrayed the city to them.
While the Huns attacked city-states along the Danube, the Vandals (led by Geiseric) captured the Western Roman province of Africa and its capital of Carthage. Africa was the richest province of the Western Empire and a main source of food for Rome. The Sassanid Shah Yazdegerd II invaded Armenia in 441.
The Romans stripped the Balkan area of forces, sending them to Sicily in order to mount an expedition against the Vandals in Africa. This left Attila and Bleda a clear path through Illyricum into the Balkans, which they invaded in 441. The Hunnish army sacked Margus and Viminacium, and then took Singidunum (Belgrade) and Sirmium. During 442, Theodosius recalled his troops from Sicily and ordered a large issue of new coins to finance operations against the Huns. He believed that he could defeat the Huns and refused the Hunnish kings' demands.
Attila responded with a campaign in 443. For the first time (as far as the Romans knew) his forces were equipped with battering rams and rolling siege towers, with which they successfully assaulted the military centers of Ratiara and Naissus (Niš) and massacred the inhabitants. Priscus said "When we arrived at Naissus we found the city deserted, as though it had been sacked; only a few sick persons lay in the churches. We halted at a short distance from the river, in an open space, for all the ground adjacent to the bank was full of the bones of men slain in war."
Advancing along the Nišava River, the Huns next took Serdica (Sofia), Philippopolis (Plovdiv), and Arcadiopolis (Lüleburgaz). They encountered and destroyed a Roman army outside Constantinople but were stopped by the double walls of the Eastern capital. They defeated a second army near Callipolis (Gelibolu).
Theodosius, unable to make effective armed resistance, admitted defeat, sending the Magister militum per Orientem Anatolius to negotiate peace terms. The terms were harsher than the previous treaty: the Emperor agreed to hand over 6,000 Roman pounds (c. 2000 kg) of gold as punishment for having disobeyed the terms of the treaty during the invasion; the yearly tribute was tripled, rising to 2,100 Roman pounds (c. 700 kg) in gold; and the ransom for each Roman prisoner rose to 12 solidi.
Their demands were met for a time, and the Hun kings withdrew into the interior of their empire. Bleda died following the Huns' withdrawal from Byzantium (probably around 445). Attila then took the throne for himself, becoming the sole ruler of the Huns.