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 largely covering the same extent of space as the modern geographical region. In its early period, the Roman province of Thrace was of this extent, but after the administrative reforms of the late 3rd century, Thracia's much reduced territory became the six small provinces which constituted the Diocese of Thrace. The medieval Byzantine theme of Thrace contained only what today is East Thrace. The largest cities of Thrace were: Plovdiv, Burgas, Stara Zagora, Sliven, Haskovo, Yambol, Komotini, Alexandroupoli, Xanthi, Edirne, Istanbul, Çorlu, Kırklareli and Tekirdağ. Most of the Bulgarian and Greek population are Orthodox Christians, while most of the Turkish