By 432, the Huns were united under Rugila. His death in 434 left his nephews Attila and Bleda (the sons of his brother Mundzuk) in control over all the united Hun tribes. At the time of their accession, the Huns were bargaining with Byzantine emperor Theodosius II's envoys over the return of several renegade tribes who had taken refuge within the Roman Empire. The following year, Attila and Bleda met with the imperial legation at Margus (present-day Požarevac) and, all seated on horseback in the Hunnic manner, negotiated a successful treaty: the Romans agreed not only to return the fugitive tribes (who had been a welcome aid against the Vandals), but also to double their previous tribute of 350 Roman pounds (ca. 114.5 kg) of gold, open their markets to Hunnish traders, and pay a ransom of eight "solidi" for each Roman taken prisoner by the Huns. The Huns, satisfied with the treaty, decamped from the empire and returned to their home, 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.