Attila and Bleda responded by renewing their campaign in 443. Striking along the Danube, they overran the military centers of Ratiaria and successfully besieged Naissus (modern Niš) with battering rams and other siege engines (military sophistication that was new to the Hun repertory), then, pushing along the Nišava, they took Serdica (Sofia), Philippopolis (Plovdiv) and Arcadiopolis (Luleburgaz). They encountered and destroyed the Roman force outside Constantinople and were only halted by their lack of siege equipment capable of breaching the city's massive walls. Theodosius admitted defeat and sent the court official Anatolius to negotiate peace terms, which were harsher than the previous treaty: the Emperor agreed to hand over 6,000 Roman pounds (ca. 1,963 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 (ca. 687 kg) in gold; and the ransom for each Roman prisoner rose to twelve "solidi."