Albanian-speakers of Western Thrace migrated towards today's European Turkey (Eastern Thrace), especially near Istanbul. Many Muslim Albanians achieved high office in Ottoman society and many of them, most notably the Köprülü family, became Grand Viziers of the Empire. The majority of the Albanian emigration came from Northern Kosovo and the Korça region of Albania. Descendants of this immigrants would later play an important role in the National Renaissance of Albania. The number of Albanians that resided in the region is unknown, as statistical data of the Ottoman Empire were based on religious identification (millets). Thus, the Orthodox Albanians were part of the Rûm millet,
Thrace (theme) Krum (r. 803–814), Omurtag (r. 814–831), and Symeon (r. 893–927) the border moved by stages south of the Balkan mountains to roughly the line of the present Bulgarian frontier with Greece and Turkey. Thus, at around the start of the 10th century, the theme comprised essentially the eastern half of modern Eastern Thrace, although it extended north along the coast to include Anchialos. From the 11th century, Thrace and Macedonia appear to have been usually combined, as attested by numerous "strategoi" and judges ("kritai") holding jurisdiction over both themes. The name fell out of use as an administrative term in