It is known that the White Croats, an early Slavic tribe, lived in the Lemko Region since the 5th and 6th centuries. It is generally accepted that the Byzantine form of Christianity was brought to the region from Constantinople by the Greek missionary brothers Constantine/Cyril and Methodius around 863. Around 899 a Byzantine Christian eparchy (diocese) was established in nearby Przemysl/Peremyshl, which included the Lemko Region.7 Since 992, political control of the region was split, roughly at the Dukla Pass, between Poland (west of the pass) and the Kievan Rus' principality of Halych (east of the pass).
The principality of Halych fell in the early 1300's. By 1340 the entire region was controlled by the Polish Commonwealth. The Polish government encouraged new settlement in the region, mostly Rus' tribes from the east and the "Vlachs" (who were probably also mostly of Rus' origin) from the south.