Facing a number of naval threats by Saracens and Byzantine Empire, the Croatian Prince Domagoj (864–876) built up the Croatian navy again and helped the coalition of emperor Louis II and the Byzantine to conquer Bari in 871. During Domagoj's reign piracy was a common practice, and he forced the Venetians to start paying tribute for sailing near the eastern Adriatic coast. After Domagoj's death, Venetian chronicles named him "The worst duke of Slavs", while Pope John VIII referred to Domagoj in letters as "Famous duke". Domagoj's son, of unknown name, ruled shortly between 876 and 878 with his brothers. They continued the rebellion, attacked the western Istrian towns in 876, but were subsequently defeated by the Venetian navy. Their ground forces defeated the Pannonian duke Kocelj (861–874) who was suzerain to the Franks, and thereby shed the Frankish vassal status. Wars of Domagoj and his son liberated Dalmatian Croats from supreme Franks rule. Zdeslav deposed him in 878 with the help of the Byzantines. He acknowledged the supreme rule of Byzantine Emperor Basil I. In 879, the Pope ask for help from prince Zdeslav for an armed escort for his delegates across southern Dalmatia and Zahumlje, but on early May 879, Zdeslav was killed near Knin in an uprising led by Branimir, a relative of Domagoj, instigated by the Roman Pope fearing Byzantine power.