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. Believing he could defeat the Huns, he refused the Hunnish kings' demands.
Attila responded with a campaign in 443.[27] Striking along the Danube, the Huns, equipped with new military weapons like the battering rams and rolling siege towers, overran the military centers of Ratiara and successfully besieged Naissus (Niš).
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, stripped of his armed forces, 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; the Hun kings withdrew into the interior of their empire. Following the Huns' withdrawal from Byzantium (probably around 445), Bleda died. Attila then took the throne for himself, becoming the sole ruler of the Huns