During his Danube sojourn (Drinkwater suggests in 255 or 256), he proclaimed his elder son Valerian II caesar and thus official heir to himself and Valerian I; the boy probably joined Gallienus on the campaign at that time, and when Gallienus moved west to the Rhine provinces in 257, he remained behind on the Danube as the personification of Imperial authority.
The Battle of Cape Ecnomus or Eknomos was a naval battle, fought off southern Sicily, in 256 BC, between the fleets of Carthage and the Roman Republic, during the First Punic War. The Carthaginian fleet was commanded by Hanno and Hamilcar; the Roman fleet jointly by the consuls for the year, Marcus Atilius Regulus and Lucius Manlius Vulso Longus.