The 9th century saw great progress in the restoration of Imperial control in the mainland, as evidenced by the participation of the bishops of Ioannina, Naupaktos, Hadrianopolis, and Vagenetia (evidently by now organized as a "Sklavinia" under imperial rule) in the Ecumenical Councils of 869/70 and 879/80. The Byzantine recovery resulted in an influx of Greeks from southern Italy and Asia Minor into the Greek interior, while remaining Slavs were Christianized and Hellenized. The eventual success of the Hellenization campaign also suggests a continuity of the original Greek population, and that the Slavs had settled among many Greeks, in contrast to areas further north, in what is now Bulgaria and the former Yugoslavia, as those areas could not be Hellenized when they were recovered by the Byzantines in the early 11th century. Following the great naval victory of admiral Nasar in 880, and the beginning of the Byzantine offensive against the Arabs in southern Italy in the 880s, the security situation improved and the Theme of Nicopolis was established, most likely after 886. As the ancient capital of Epirus had been laid waste by the Slavs, the capital of the new theme became Naupaktos further south. The extent of the new province is unclear, but probably matched the extent of the Metropolis of Naupaktos, established at about the same time, encompassing the sees of Vonditsa, Aetos, Acheloos, Rogoi, Ioannina, Hadrianopolis, Photike, and Buthrotum. Vagenetia notably no longer appears as a bishopric. As the authors of the "Tabula Imperii Byzantini" comment, it appears that "the Byzantine administration had brought the strongly Slavic-settled areas in the mainland somewhat under its control, and a certain Re-Hellenization had set in". Further north, the region around Dyrrhachium existed as the homonymous theme possibly as early as the 9th century.